Update RootFrameViewport::userScroll to distribute scrolls between viewports.

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

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 98 matching lines @@
     EXPECT_CALL(*scrollableArea, minimumScrollPosition()).Times(AtLeast(1)).WillRepeatedly(Return(IntPoint()));
     EXPECT_CALL(*scrollableArea, maximumScrollPosition()).Times(AtLeast(1)).WillRepeatedly(Return(IntPoint(1000, 1000)));
     EXPECT_CALL(*scrollableArea, setScrollOffset(_, _)).Times(12);
     EXPECT_CALL(*scrollableArea, registerForAnimation()).Times(3);
 
     EXPECT_FALSE(scrollAnimator->hasRunningAnimation());
 
     ScrollResultOneDimensional result = scrollAnimator->userScroll(HorizontalScrollbar, ScrollByLine, 100, -1);
     EXPECT_FALSE(scrollAnimator->hasRunningAnimation());
     EXPECT_FALSE(result.didScroll);
-    EXPECT_FLOAT_EQ(-100.0, result.unusedScrollDelta);
+    EXPECT_FLOAT_EQ(-1.0f, result.unusedScrollDelta);
 
     result = scrollAnimator->userScroll(HorizontalScrollbar, ScrollByLine, 100, 1);
     EXPECT_TRUE(scrollAnimator->hasRunningAnimation());
     EXPECT_TRUE(result.didScroll);
     EXPECT_FLOAT_EQ(0.0, result.unusedScrollDelta);
 
     gMockedTime += 0.05;
     scrollAnimator->serviceScrollAnimations();
 
     EXPECT_NE(100, scrollAnimator->currentPosition().x());
@@ skipping 64 matching lines @@
     EXPECT_EQ(0, scrollAnimator->currentPosition().y());
     reset(*scrollAnimator);
 
     scrollAnimator->userScroll(HorizontalScrollbar, ScrollByPixel, 100, 1);
     EXPECT_EQ(100, scrollAnimator->currentPosition().x());
     EXPECT_EQ(0, scrollAnimator->currentPosition().y());
     reset(*scrollAnimator);
 }
 
 } // namespace blink