Explicitly allocate and deallocate our initial computed values.

This allows us to trigger style struct destructors before Gecko's leak checking
runs.

components/style/properties/gecko.mako.rs

@@ -100,7 +100,30 @@ impl ComputedValues {
         ComputedValues::inherit_from(parent)
     }
 
-    pub fn initial_values() -> &'static Self { &*INITIAL_GECKO_VALUES }
+    pub fn initial_values() -> &'static Self {
+        unsafe {
+            debug_assert!(!INITIAL_GECKO_VALUES.is_null());
+            &*INITIAL_GECKO_VALUES
+        }
+    }
+
+    pub unsafe fn initialize() {
+        debug_assert!(INITIAL_GECKO_VALUES.is_null());
+        INITIAL_GECKO_VALUES = Box::into_raw(Box::new(ComputedValues {
+            % for style_struct in data.style_structs:
+               ${style_struct.ident}: style_structs::${style_struct.name}::initial(),
+            % endfor
+            custom_properties: None,
+            shareable: true,
+            writing_mode: WritingMode::empty(),
+            root_font_size: longhands::font_size::get_initial_value(),
+        }));
+    }
+
+    pub unsafe fn shutdown() {
+        debug_assert!(!INITIAL_GECKO_VALUES.is_null());
+        let _ = Box::from_raw(INITIAL_GECKO_VALUES);
+    }
 
     #[inline]
     pub fn do_cascade_property<F: FnOnce(&[CascadePropertyFn])>(f: F) {
@@ -1338,17 +1361,7 @@ ${impl_style_struct(style_struct)}
 ${define_ffi_struct_accessor(style_struct)}
 % endfor
 
-lazy_static! {
+static mut INITIAL_GECKO_VALUES: *mut ComputedValues = 0 as *mut ComputedValues;
-    pub static ref INITIAL_GECKO_VALUES: ComputedValues = ComputedValues {
-        % for style_struct in data.style_structs:
-           ${style_struct.ident}: style_structs::${style_struct.name}::initial(),
-        % endfor
-        custom_properties: None,
-        shareable: true,
-        writing_mode: WritingMode::empty(),
-        root_font_size: longhands::font_size::get_initial_value(),
-    };
-}
 
 static CASCADE_PROPERTY: [CascadePropertyFn; ${len(data.longhands)}] = [
     % for property in data.longhands:

ports/geckolib/gecko_bindings/bindings.rs

@@ -368,6 +368,7 @@ extern "C" {
     pub fn Servo_AddRefComputedValues(arg1: *mut ServoComputedValues);
     pub fn Servo_ReleaseComputedValues(arg1: *mut ServoComputedValues);
     pub fn Servo_Initialize();
+    pub fn Servo_Shutdown();
     pub fn Servo_RestyleDocument(doc: *mut RawGeckoDocument,
                                  set: *mut RawServoStyleSet);
     pub fn Servo_RestyleSubtree(node: *mut RawGeckoNode,

ports/geckolib/glue.rs

@@ -76,6 +76,15 @@ pub extern "C" fn Servo_Initialize() -> () {
     //
     // See https://doc.rust-lang.org/log/env_logger/index.html for instructions.
     env_logger::init().unwrap();
+
+    // Allocate our default computed values.
+    unsafe { ComputedValues::initialize(); }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Shutdown() -> () {
+    // Destroy our default computed values.
+    unsafe { ComputedValues::shutdown(); }
 }
 
 fn restyle_subtree(node: GeckoNode, raw_data: *mut RawServoStyleSet) {