Add test for replacing a composited animation

CL 1715764 introduced a performance regression, where a replaced
animation would not be composited for the initial frame.  This was
caused by a bug in calculation of the pending state, which in turn
caused a replaced animation to be flagged as incompatible.  The bug was
fixed in CL 1728074. This patch introduced a test to ensure that the fix
does not regress.

Bug: 992408
Change-Id: Iab210ca9b525773ebb2c0a6f28d63f25c0b574e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2080445Reviewed-by: Majid Valipour <majidvp@chromium.org>
Commit-Queue: Kevin Ellis <kevers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745970}

third_party/blink/renderer/core/animation/animation_test.cc

@@ -137,6 +137,10 @@ class AnimationAnimationTestNoCompositing : public RenderingTest {
 
     SetBodyInnerHTML("<div id='target'></div>");
 
+    MakeCompositedAnimation();
+  }
+
+  void MakeCompositedAnimation() {
     // Create a compositable animation; in this case opacity from 1 to 0.
     Timing timing;
     timing.iteration_duration = AnimationTimeDelta::FromSecondsD(30);
@@ -1329,6 +1333,22 @@ TEST_F(AnimationAnimationTestCompositing, PreCommitRecordsHistograms) {
   }
 }
 
+// crbug.com/990000.
+TEST_F(AnimationAnimationTestCompositing, ReplaceCompositedAnimation) {
+  const std::string histogram_name =
+      "Blink.Animation.CompositedAnimationFailureReason";
+
+  // Start with a composited animation.
+  ResetWithCompositedAnimation();
+  ASSERT_TRUE(animation->HasActiveAnimationsOnCompositor());
+
+  // Replace the animation. The new animation should not be incompatible and
+  // therefore able to run on the compositor.
+  animation->cancel();
+  MakeCompositedAnimation();
+  ASSERT_TRUE(animation->HasActiveAnimationsOnCompositor());
+}
+
 TEST_F(AnimationAnimationTestCompositing, SetKeyframesCausesCompositorPending) {
   ResetWithCompositedAnimation();