Bug 1308099 part 1 - Rename AnimationPhase::Null to AnimationPhase::Idle. r=hiro

In Web Animations specification, if the animation effect is in none of the any phase, it define as 'Idle' phase. [1]
But, in the gecko, it defined as 'Null' phase.

So we will need to use 'Idle' phase for consistency.

[1] https://w3c.github.io/web-animations/#idle-phase

MozReview-Commit-ID: FlPpYOqdM4X

--HG--
extra : rebase_source : ec294c84f9c77a42d6128e3d43380b80fc130513

dom/animation/ComputedTiming.h

@@ -64,12 +64,12 @@ struct ComputedTiming
   }
 
   enum class AnimationPhase {
-    Null,   // Not sampled (null sample time)
+    Idle,   // Not sampled (null sample time)
     Before, // Sampled prior to the start of the active interval
     Active, // Sampled within the active interval
     After   // Sampled after (or at) the end of the active interval
   };
-  AnimationPhase      mPhase = AnimationPhase::Null;
+  AnimationPhase      mPhase = AnimationPhase::Idle;
 
   ComputedTimingFunction::BeforeFlag mBeforeFlag =
     ComputedTimingFunction::BeforeFlag::Unset;

layout/style/nsAnimationManager.cpp

@@ -229,7 +229,7 @@ CSSAnimation::QueueEvents()
 
   AutoTArray<AnimationEventParams, 2> events;
   switch (mPreviousPhase) {
-    case AnimationPhase::Null:
+    case AnimationPhase::Idle:
     case AnimationPhase::Before:
       if (currentPhase == AnimationPhase::Active) {
         events.AppendElement(AnimationEventParams{ eAnimationStart,

layout/style/nsAnimationManager.h

@@ -76,7 +76,7 @@ public:
     , mIsStylePaused(false)
     , mPauseShouldStick(false)
     , mNeedsNewAnimationIndexWhenRun(false)
-    , mPreviousPhase(ComputedTiming::AnimationPhase::Null)
+    , mPreviousPhase(ComputedTiming::AnimationPhase::Idle)
     , mPreviousIteration(0)
   {
     // We might need to drop this assertion once we add a script-accessible

layout/style/nsTransitionManager.h

@@ -272,7 +272,7 @@ protected:
   // to be queued on this tick.
   // See: https://drafts.csswg.org/css-transitions-2/#transition-phase
   enum class TransitionPhase {
-    Idle   = static_cast<int>(ComputedTiming::AnimationPhase::Null),
+    Idle   = static_cast<int>(ComputedTiming::AnimationPhase::Idle),
     Before = static_cast<int>(ComputedTiming::AnimationPhase::Before),
     Active = static_cast<int>(ComputedTiming::AnimationPhase::Active),
     After  = static_cast<int>(ComputedTiming::AnimationPhase::After),