Introduce and start using the MallocSizeOf trait.

MallocSizeOf is similar to the existing HeapSizeOf trait from the
heapsize crate. The only difference is that MallocSizeOf's
malloc_size_of_children() function takes an additional MallocSizeOfFn
argument, which is used to measure heap blocks. This extra argument
makes MallocSizeOf match how Gecko's memory measurements work, and is
required for Stylo to integrate with DMD.

The patch also introduces a second trait, MallocSizeOfWithGuard, which
is much the same as MallocSizeOf, but with a |guard| argument for the
global style lock.

Finally, the patch uses the new traits to measure a small amount of
Stylo's memory usage.

components/style/gecko/generated/bindings.rs

@@ -39,6 +39,7 @@ use gecko_bindings::structs::FontSizePrefs;
 use gecko_bindings::structs::GeckoFontMetrics;
 use gecko_bindings::structs::IterationCompositeOperation;
 use gecko_bindings::structs::Keyframe;
+use gecko_bindings::structs::MallocSizeOf;
 use gecko_bindings::structs::ServoBundledURI;
 use gecko_bindings::structs::ServoElementSnapshot;
 use gecko_bindings::structs::ServoElementSnapshotTable;
@@ -1765,6 +1766,11 @@ extern "C" {
     pub fn Servo_StyleSheet_Clone(sheet: RawServoStyleSheetBorrowed)
      -> RawServoStyleSheetStrong;
 }
+extern "C" {
+    pub fn Servo_StyleSheet_SizeOfIncludingThis(malloc_size_of: MallocSizeOf,
+                                                sheet: RawServoStyleSheetBorrowed)
+     -> usize;
+}
 extern "C" {
     pub fn Servo_StyleSet_Init(pres_context: RawGeckoPresContextOwned)
      -> RawServoStyleSetOwned;

components/style/properties/declaration_block.rs

@@ -16,6 +16,7 @@ use std::fmt;
 use std::slice::Iter;
 use style_traits::ToCss;
 use stylesheets::{CssRuleType, Origin, UrlExtraData};
+use stylesheets::{MallocSizeOf, MallocSizeOfFn};
 use super::*;
 #[cfg(feature = "gecko")] use properties::animated_properties::AnimationValueMap;
 
@@ -46,6 +47,12 @@ pub enum Importance {
     Important,
 }
 
+impl MallocSizeOf for Importance {
+    fn malloc_size_of_children(&self, _malloc_size_of: MallocSizeOfFn) -> usize {
+        0
+    }
+}
+
 impl Importance {
     /// Return whether this is an important declaration.
     pub fn important(self) -> bool {
@@ -70,6 +77,12 @@ pub struct PropertyDeclarationBlock {
     longhands: LonghandIdSet,
 }
 
+impl MallocSizeOf for PropertyDeclarationBlock {
+    fn malloc_size_of_children(&self, malloc_size_of: MallocSizeOfFn) -> usize {
+        self.declarations.malloc_size_of_children(malloc_size_of)
+    }
+}
+
 /// Iterator for PropertyDeclaration to be generated from PropertyDeclarationBlock.
 #[derive(Clone)]
 pub struct PropertyDeclarationIterator<'a> {

components/style/properties/properties.mako.rs

@@ -35,7 +35,7 @@ use properties::animated_properties::TransitionProperty;
 #[cfg(feature = "servo")] use servo_config::prefs::PREFS;
 use shared_lock::StylesheetGuards;
 use style_traits::{HasViewportPercentage, ToCss};
-use stylesheets::{CssRuleType, Origin, UrlExtraData};
+use stylesheets::{CssRuleType, MallocSizeOf, MallocSizeOfFn, Origin, UrlExtraData};
 #[cfg(feature = "servo")] use values::Either;
 use values::computed;
 use cascade_info::CascadeInfo;
@@ -1171,6 +1171,14 @@ impl ToCss for PropertyDeclaration {
     % endif
 </%def>
 
+impl MallocSizeOf for PropertyDeclaration {
+    fn malloc_size_of_children(&self, _malloc_size_of: MallocSizeOfFn) -> usize {
+        // The variants of PropertyDeclaration mostly (entirely?) contain
+        // scalars, so this is reasonable.
+        0
+    }
+}
+
 impl PropertyDeclaration {
     /// Given a property declaration, return the property declaration id.
     pub fn id(&self) -> PropertyDeclarationId {

components/style/stylesheets.rs

@@ -40,6 +40,8 @@ use shared_lock::{SharedRwLock, Locked, ToCssWithGuard, SharedRwLockReadGuard};
 use std::borrow::Borrow;
 use std::cell::Cell;
 use std::fmt;
+use std::mem::align_of;
+use std::os::raw::c_void;
 use std::sync::atomic::{AtomicBool, Ordering};
 use str::starts_with_ignore_ascii_case;
 use style_traits::ToCss;
@@ -99,6 +101,57 @@ pub struct Namespaces {
     pub prefixes: FnvHashMap<Prefix , Namespace>,
 }
 
+/// Like gecko_bindings::structs::MallocSizeOf, but without the Option<> wrapper. Note that
+/// functions of this type should not be called via do_malloc_size_of(), rather than directly.
+pub type MallocSizeOfFn = unsafe extern "C" fn(ptr: *const c_void) -> usize;
+
+/// Call malloc_size_of on ptr, first checking that the allocation isn't empty.
+pub unsafe fn do_malloc_size_of<T>(malloc_size_of: MallocSizeOfFn, ptr: *const T) -> usize {
+    if ptr as usize <= align_of::<T>() {
+        0
+    } else {
+        malloc_size_of(ptr as *const c_void)
+    }
+}
+
+/// Trait for measuring the size of heap data structures.
+pub trait MallocSizeOf {
+    /// Measure the size of any heap-allocated structures that hang off this value, but not the
+    /// space taken up by the value itself.
+    fn malloc_size_of_children(&self, malloc_size_of: MallocSizeOfFn) -> usize;
+}
+
+/// Like MallocSizeOf, but operates with the global SharedRwLockReadGuard locked.
+pub trait MallocSizeOfWithGuard {
+    /// Like MallocSizeOf::malloc_size_of_children, but with a |guard| argument.
+    fn malloc_size_of_children(&self, guard: &SharedRwLockReadGuard,
+                               malloc_size_of: MallocSizeOfFn) -> usize;
+}
+
+impl<A: MallocSizeOf, B: MallocSizeOf> MallocSizeOf for (A, B) {
+    fn malloc_size_of_children(&self, malloc_size_of: MallocSizeOfFn) -> usize {
+        self.0.malloc_size_of_children(malloc_size_of) +
+            self.1.malloc_size_of_children(malloc_size_of)
+    }
+}
+
+impl<T: MallocSizeOf> MallocSizeOf for Vec<T> {
+    fn malloc_size_of_children(&self, malloc_size_of: MallocSizeOfFn) -> usize {
+        self.iter().fold(
+            unsafe { do_malloc_size_of(malloc_size_of, self.as_ptr()) },
+            |n, elem| n + elem.malloc_size_of_children(malloc_size_of))
+    }
+}
+
+impl<T: MallocSizeOfWithGuard> MallocSizeOfWithGuard for Vec<T> {
+    fn malloc_size_of_children(&self, guard: &SharedRwLockReadGuard,
+                               malloc_size_of: MallocSizeOfFn) -> usize {
+        self.iter().fold(
+            unsafe { do_malloc_size_of(malloc_size_of, self.as_ptr()) },
+            |n, elem| n + elem.malloc_size_of_children(guard, malloc_size_of))
+    }
+}
+
 /// A list of CSS rules.
 #[derive(Debug)]
 pub struct CssRules(pub Vec<CssRule>);
@@ -119,6 +172,13 @@ impl CssRules {
     }
 }
 
+impl MallocSizeOfWithGuard for CssRules {
+    fn malloc_size_of_children(&self, guard: &SharedRwLockReadGuard,
+                               malloc_size_of: MallocSizeOfFn) -> usize {
+        self.0.malloc_size_of_children(guard, malloc_size_of)
+    }
+}
+
 #[allow(missing_docs)]
 pub enum RulesMutateError {
     Syntax,
@@ -254,9 +314,9 @@ impl CssRulesHelpers for Arc<Locked<CssRules>> {
 
         Ok(new_rule)
     }
-
 }
 
+
 /// The structure servo uses to represent a stylesheet.
 #[derive(Debug)]
 pub struct Stylesheet {
@@ -281,6 +341,13 @@ pub struct Stylesheet {
     pub quirks_mode: QuirksMode,
 }
 
+impl MallocSizeOfWithGuard for Stylesheet {
+    fn malloc_size_of_children(&self, guard: &SharedRwLockReadGuard,
+                               malloc_size_of: MallocSizeOfFn) -> usize {
+        // Measurement of other fields may be added later.
+        self.rules.read_with(guard).malloc_size_of_children(guard, malloc_size_of)
+    }
+}
 
 /// This structure holds the user-agent and user stylesheets.
 pub struct UserAgentStylesheets {
@@ -315,6 +382,28 @@ pub enum CssRule {
     Document(Arc<Locked<DocumentRule>>),
 }
 
+impl MallocSizeOfWithGuard for CssRule {
+    fn malloc_size_of_children(&self, guard: &SharedRwLockReadGuard,
+                               malloc_size_of: MallocSizeOfFn) -> usize {
+        match *self {
+            CssRule::Style(ref lock) => {
+                lock.read_with(guard).malloc_size_of_children(guard, malloc_size_of)
+            },
+            // Measurement of these fields may be added later.
+            CssRule::Import(_) => 0,
+            CssRule::Media(_) => 0,
+            CssRule::FontFace(_) => 0,
+            CssRule::CounterStyle(_) => 0,
+            CssRule::Keyframes(_) => 0,
+            CssRule::Namespace(_) => 0,
+            CssRule::Viewport(_) => 0,
+            CssRule::Supports(_) => 0,
+            CssRule::Page(_) => 0,
+            CssRule::Document(_)  => 0,
+        }
+    }
+}
+
 #[allow(missing_docs)]
 #[derive(PartialEq, Eq, Copy, Clone)]
 pub enum CssRuleType {
@@ -825,6 +914,14 @@ pub struct StyleRule {
     pub source_location: SourceLocation,
 }
 
+impl MallocSizeOfWithGuard for StyleRule {
+    fn malloc_size_of_children(&self, guard: &SharedRwLockReadGuard,
+                               malloc_size_of: MallocSizeOfFn) -> usize {
+        // Measurement of other fields may be added later.
+        self.block.read_with(guard).malloc_size_of_children(malloc_size_of)
+    }
+}
+
 impl ToCssWithGuard for StyleRule {
     // https://drafts.csswg.org/cssom/#serialize-a-css-rule CSSStyleRule
     fn to_css<W>(&self, guard: &SharedRwLockReadGuard, dest: &mut W) -> fmt::Result