Communicate MT changes to impl-only scroll offset animations

third_party/WebKit/Source/platform/scroll/ScrollAnimatorCompositorCoordinator.h

Index: third_party/WebKit/Source/platform/scroll/ScrollAnimatorCompositorCoordinator.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollAnimatorCompositorCoordinator.h b/third_party/WebKit/Source/platform/scroll/ScrollAnimatorCompositorCoordinator.h
index 9b69df747f69c2eef0b5c786e4b457f06511894c..4346dce09a3ff5f43559f287fe14a4c9381105a5 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollAnimatorCompositorCoordinator.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollAnimatorCompositorCoordinator.h
@@ -7,6 +7,7 @@
 
 #include "base/gtest_prod_util.h"
 #include "cc/animation/animation_curve.h"
+#include "cc/animation/scroll_offset_animations.h"
 #include "platform/PlatformExport.h"
 #include "platform/animation/CompositorAnimationDelegate.h"
 #include "platform/animation/CompositorAnimationPlayerClient.h"
@@ -33,6 +34,8 @@ public:
     void dispose();
     String runStateAsText() const;
 
+    void updateImplOnlyScrollOffsetAnimation(const FloatSize& adjustment);
+
     virtual bool hasRunningAnimation() const { return false; }
 
     virtual void resetAnimationState();
@@ -41,10 +44,10 @@ public:
     // and continues it on the main thread. This should only be called when in
     // DocumentLifecycle::LifecycleState::CompositingClean state.
     virtual void takeoverCompositorAnimation();
+    virtual void updateCompositorAnimations();
 
     virtual ScrollableArea* getScrollableArea() const = 0;
     virtual void tickAnimation(double monotonicTime) = 0;
-    virtual void updateCompositorAnimations() = 0;
     virtual void notifyCompositorAnimationFinished(int groupId) = 0;
     virtual void notifyCompositorAnimationAborted(int groupId) = 0;
     virtual void layerForCompositedScrollingDidChange(CompositorAnimationTimeline*) = 0;
@@ -82,6 +85,7 @@ protected:
     FRIEND_TEST_ALL_PREFIXES(ScrollAnimatorTest, AnimatedScrollTakeover);
     FRIEND_TEST_ALL_PREFIXES(ScrollAnimatorTest, CancellingAnimationResetsState);
     FRIEND_TEST_ALL_PREFIXES(ScrollAnimatorTest, CancellingCompositorAnimation);
+    FRIEND_TEST_ALL_PREFIXES(ScrollAnimatorTest, ImplOnlyAnimationUpdatesCleared);
 
     enum class RunState {
         // No animation.
@@ -127,6 +131,10 @@ protected:
     RunState m_runState;
     int m_compositorAnimationId;
     int m_compositorAnimationGroupId;
+
+    // A list of updates that happened on the main thread that may change
+    // impl-only scroll offset animations.
+    std::vector<FloatSize> m_implOnlyAnimationAdjustments;
 };
 
 } // namespace blink