Bug 1004871 part 5 - Add ComputedTiming data structure; r=dholbert

This patch adds a ComputedTiming struct for storing the results of calculating
the timing properties of an animation at a given sample time.

layout/style/AnimationCommon.cpp

@@ -362,6 +362,10 @@ ComputedTimingFunction::GetValue(double aPortion) const
 
 } /* end sub-namespace css */
 
+// In the Web Animations model, the time fraction can be outside the range
+// [0.0, 1.0] but it shouldn't be Infinity.
+const double ComputedTiming::kNullTimeFraction = NS_IEEEPositiveInfinity();
+
 bool
 ElementAnimation::IsRunningAt(TimeStamp aTime) const
 {

layout/style/AnimationCommon.h

@@ -243,6 +243,37 @@ struct AnimationTiming
   }
 };
 
+/**
+ * Stores the results of calculating the timing properties of an animation
+ * at a given sample time.
+ */
+struct ComputedTiming
+{
+  ComputedTiming()
+  : mTimeFraction(kNullTimeFraction),
+    mCurrentIteration(0)
+  { }
+
+  static const double kNullTimeFraction;
+
+  // Will be kNullTimeFraction if the animation is neither animating nor
+  // filling at the sampled time.
+  double mTimeFraction;
+
+  // Zero-based iteration index (meaningless if mTimeFraction is
+  // kNullTimeFraction).
+  uint64_t mCurrentIteration;
+
+  enum {
+    // Sampled prior to the start of the active interval
+    AnimationPhase_Before,
+    // Sampled within the active interval
+    AnimationPhase_Active,
+    // Sampled after (or at) the end of the active interval
+    AnimationPhase_After
+  } mPhase;
+};
+
 /**
  * Data about one animation (i.e., one of the values of
  * 'animation-name') running on an element.