style: Add a new Timer structure to the shared style context, and basic infrastructure for controlling animations.

components/script/dom/testbinding.rs

@@ -581,6 +581,10 @@ impl TestBindingMethods for TestBinding {
         }
     }
 
+    fn AdvanceClock(&self, ms: i32) {
+        self.global().r().as_window().advance_animation_clock(ms);
+    }
+
     fn Panic(&self) { panic!("explicit panic from script") }
 }
 

components/script/dom/webidls/TestBinding.webidl

@@ -424,6 +424,8 @@ interface TestBinding {
   static void prefControlledStaticMethodDisabled();
   [Pref="dom.testbinding.prefcontrolled.enabled"]
   const unsigned short prefControlledConstDisabled = 0;
+  [Pref="layout.animations.test.enabled"]
+  void advanceClock(long millis);
 
   [Pref="dom.testbinding.prefcontrolled2.enabled"]
   readonly attribute boolean prefControlledAttributeEnabled;

components/script/dom/window.rs

@@ -1030,6 +1030,12 @@ impl Window {
         recv.recv().unwrap_or((Size2D::zero(), Point2D::zero()))
     }
 
+    /// Advances the layout animation clock by `delta` milliseconds, and then
+    /// forces a reflow.
+    pub fn advance_animation_clock(&self, delta: i32) {
+        self.layout_chan.send(Msg::AdvanceClockMs(delta)).unwrap();
+    }
+
     /// Reflows the page unconditionally if possible and not suppressed. This
     /// method will wait for the layout thread to complete (but see the `TODO`
     /// below). If there is no window size yet, the page is presumed invisible