Don't skip a frame when running smooth scroll animation on the main thread

third_party/WebKit/Source/platform/scroll/ScrollAnimatorTest.cpp

Index: third_party/WebKit/Source/platform/scroll/ScrollAnimatorTest.cpp
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollAnimatorTest.cpp b/third_party/WebKit/Source/platform/scroll/ScrollAnimatorTest.cpp
index e0f29e0435a4f515670f4dd4677c72e592abf204..976a456e9e33db9bf47cdd81cfa1c5b35f723157 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollAnimatorTest.cpp
+++ b/third_party/WebKit/Source/platform/scroll/ScrollAnimatorTest.cpp
@@ -88,6 +88,16 @@ public:
         animator = scrollAnimator;
     }
 
+    bool shouldScrollOnMainThread() const override
+    {
+        return m_scrollOnMainThread;
+    }
+
+    void setScrollOnMainThread(bool scrollOnMainThread)
+    {
+        m_scrollOnMainThread = scrollOnMainThread;
+    }
+
     DoublePoint scrollPositionDouble() const override
     {
         if (animator)
@@ -114,6 +124,7 @@ private:
         : m_scrollAnimatorEnabled(scrollAnimatorEnabled) { }
 
     bool m_scrollAnimatorEnabled;
+    bool m_scrollOnMainThread = false;
     Member<ScrollAnimator> animator;
 };
 
@@ -157,6 +168,7 @@ static void reset(ScrollAnimator& scrollAnimator)
 TEST(ScrollAnimatorTest, MainThreadStates)
 {
     MockScrollableArea* scrollableArea = MockScrollableArea::create(true);
+    scrollableArea->setScrollOnMainThread(true);
     ScrollAnimator* scrollAnimator = new ScrollAnimator(scrollableArea, getMockedTime);
 
     EXPECT_CALL(*scrollableArea, minimumScrollPosition()).Times(AtLeast(1))
@@ -164,7 +176,8 @@ TEST(ScrollAnimatorTest, MainThreadStates)
     EXPECT_CALL(*scrollableArea, maximumScrollPosition()).Times(AtLeast(1))
         .WillRepeatedly(Return(IntPoint(1000, 1000)));
     EXPECT_CALL(*scrollableArea, setScrollOffset(_, _)).Times(2);
-    EXPECT_CALL(*scrollableArea, registerForAnimation()).Times(2);
+    // Once from userScroll.
+    EXPECT_CALL(*scrollableArea, registerForAnimation()).Times(1);
     EXPECT_CALL(*scrollableArea, scheduleAnimation()).Times(AtLeast(1))
         .WillRepeatedly(Return(true));
 
@@ -176,7 +189,7 @@ TEST(ScrollAnimatorTest, MainThreadStates)
     // WaitingToSendToCompositor
     scrollAnimator->userScroll(ScrollByLine, FloatSize(10, 0));
     EXPECT_EQ(scrollAnimator->m_runState,
-        ScrollAnimatorCompositorCoordinator::RunState::WaitingToSendToCompositor);
+        ScrollAnimatorCompositorCoordinator::RunState::RunningOnMainThread);
 
     // RunningOnMainThread
     gMockedTime += 0.05;
@@ -199,6 +212,9 @@ TEST(ScrollAnimatorTest, MainThreadStates)
         ScrollAnimatorCompositorCoordinator::RunState::Idle);
 
     reset(*scrollAnimator);
+
+    // Forced GC in order to finalize objects depending on the mock object.
+    ThreadHeap::collectAllGarbage();
 }
 
 TEST(ScrollAnimatorTest, MainThreadEnabled)