Bug 1036287 part 1 - Add a null animation phase; r=dholbert

In order to support arbitrary timelines which may provide a "null" current time,
we need a suitable value to return from GetComputedTimingAt for the animation's
phase when the timeline time is null.

This patch introduces a null animation phase for this purpose.

layout/style/AnimationCommon.h

@@ -270,17 +270,13 @@ struct AnimationTiming
 /**
  * Stores the results of calculating the timing properties of an animation
  * at a given sample time.
- *
- * The members of a default-constructed object of this type are not meaningful.
- * Rather, this object is intended to be used as the return value of
- * ElementAnimation::GetComputedTimingAt which ensures all members are set
- * correctly.
  */
 struct ComputedTiming
 {
   ComputedTiming()
-  : mTimeFraction(kNullTimeFraction),
-    mCurrentIteration(0)
+  : mTimeFraction(kNullTimeFraction)
+  , mCurrentIteration(0)
+  , mPhase(AnimationPhase_Null)
   { }
 
   static const double kNullTimeFraction;
@@ -298,6 +294,8 @@ struct ComputedTiming
   uint64_t mCurrentIteration;
 
   enum {
+    // Not sampled (null sample time)
+    AnimationPhase_Null,
     // Sampled prior to the start of the active interval
     AnimationPhase_Before,
     // Sampled within the active interval

layout/style/nsAnimationManager.cpp

@@ -48,6 +48,7 @@ nsAnimationManager::GetEventsAt(ElementAnimationCollection* aCollection,
       ElementAnimation::GetComputedTimingAt(localTime, anim->mTiming);
 
     switch (computedTiming.mPhase) {
+      case ComputedTiming::AnimationPhase_Null:
       case ComputedTiming::AnimationPhase_Before:
         // Do nothing
         break;