CC: Clamp opacity values during an animation

Opacity values should be clipped between [0,1] in a composited animation.

BUG=400869

Review URL: https://codereview.chromium.org/474803002

Cr-Commit-Position: refs/heads/master@{#289746}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289746 0039d316-1c4b-4281-b951-d872f2087c98

cc/animation/layer_animation_controller.cc

@@ -854,7 +854,8 @@ void LayerAnimationController::TickAnimations(base::TimeTicks monotonic_time) {
         case Animation::Opacity: {
           const FloatAnimationCurve* float_animation_curve =
               animations_[i]->curve()->ToFloatAnimationCurve();
-          const float opacity = float_animation_curve->GetValue(trimmed);
+          const float opacity = std::max(
+              std::min(float_animation_curve->GetValue(trimmed), 1.0f), 0.f);
           NotifyObserversOpacityAnimated(
               opacity,
               animations_[i]->affects_active_observers(),

cc/animation/layer_animation_controller_unittest.cc

@@ -2085,6 +2085,38 @@ TEST(LayerAnimationControllerTest, ActivationBetweenAnimateAndUpdateState) {
   EXPECT_EQ(0.75f, dummy_impl.opacity());
 }
 
+TEST(LayerAnimationControllerTest, ClippedOpacityValues) {
+  FakeLayerAnimationValueObserver dummy;
+  scoped_refptr<LayerAnimationController> controller(
+      LayerAnimationController::Create(0));
+  controller->AddValueObserver(&dummy);
+
+  AddOpacityTransitionToController(controller.get(), 1, 1.f, 2.f, true);
+
+  controller->Animate(kInitialTickTime);
+  EXPECT_EQ(1.f, dummy.opacity());
+
+  // Opacity values are clipped [0,1]
+  controller->Animate(kInitialTickTime + TimeDelta::FromMilliseconds(1000));
+  EXPECT_EQ(1.f, dummy.opacity());
+}
+
+TEST(LayerAnimationControllerTest, ClippedNegativeOpacityValues) {
+  FakeLayerAnimationValueObserver dummy;
+  scoped_refptr<LayerAnimationController> controller(
+      LayerAnimationController::Create(0));
+  controller->AddValueObserver(&dummy);
+
+  AddOpacityTransitionToController(controller.get(), 1, 0.f, -2.f, true);
+
+  controller->Animate(kInitialTickTime);
+  EXPECT_EQ(0.f, dummy.opacity());
+
+  // Opacity values are clipped [0,1]
+  controller->Animate(kInitialTickTime + TimeDelta::FromMilliseconds(1000));
+  EXPECT_EQ(0.f, dummy.opacity());
+}
+
 TEST(LayerAnimationControllerTest, PushedDeletedAnimationWaitsForActivation) {
   scoped_ptr<AnimationEventsVector> events(
       make_scoped_ptr(new AnimationEventsVector));