Move root_font_size to the device

components/style/gecko/media_queries.rs

@@ -17,7 +17,9 @@ use gecko_bindings::structs::RawGeckoPresContextOwned;
 use media_queries::MediaType;
 use parser::ParserContext;
 use properties::{ComputedValues, StyleBuilder};
+use properties::longhands::font_size;
 use std::fmt::{self, Write};
+use std::sync::atomic::{AtomicIsize, Ordering};
 use str::starts_with_ignore_ascii_case;
 use string_cache::Atom;
 use style_traits::ToCss;
@@ -35,8 +37,20 @@ pub struct Device {
     pub pres_context: RawGeckoPresContextOwned,
     default_values: Arc<ComputedValues>,
     viewport_override: Option<ViewportConstraints>,
+    /// The font size of the root element
+    /// This is set when computing the style of the root
+    /// element, and used for rem units in other elements.
+    ///
+    /// When computing the style of the root element, there can't be any
+    /// other style being computed at the same time, given we need the style of
+    /// the parent to compute everything else. So it is correct to just use
+    /// a relaxed atomic here.
+    root_font_size: AtomicIsize,
 }
 
+unsafe impl Sync for Device {}
+unsafe impl Send for Device {}
+
 impl Device {
     /// Trivially constructs a new `Device`.
     pub fn new(pres_context: RawGeckoPresContextOwned) -> Self {
@@ -45,6 +59,7 @@ impl Device {
             pres_context: pres_context,
             default_values: ComputedValues::default_values(unsafe { &*pres_context }),
             viewport_override: None,
+            root_font_size: AtomicIsize::new(font_size::get_initial_value().0 as isize), // FIXME(bz): Seems dubious?
         }
     }
 
@@ -73,6 +88,16 @@ impl Device {
         &self.default_values
     }
 
+    /// Get the font size of the root element (for rem)
+    pub fn root_font_size(&self) -> Au {
+        Au::new(self.root_font_size.load(Ordering::Relaxed) as i32)
+    }
+
+    /// Set the font size of the root element (for rem)
+    pub fn set_root_font_size(&self, size: Au) {
+        self.root_font_size.store(size.0 as isize, Ordering::Relaxed)
+    }
+
     /// Recreates all the temporary state that the `Device` stores.
     ///
     /// This includes the viewport override from `@viewport` rules, and also the
@@ -111,9 +136,6 @@ impl Device {
     }
 }
 
-unsafe impl Sync for Device {}
-unsafe impl Send for Device {}
-
 /// A expression for gecko contains a reference to the media feature, the value
 /// the media query contained, and the range to evaluate.
 #[derive(Debug, Clone)]