Don't set shownRatio in main thread top controls on animated state change.

third_party/WebKit/Source/web/tests/TopControlsTest.cpp

 /*
  * Copyright (C) 2015 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 541 matching lines @@
 
     verticalScroll(-50.f);
     EXPECT_FLOAT_EQ(0, webView->topControls().contentOffset());
     EXPECT_POINT_EQ(IntPoint(0, 90), frame()->view()->scrollPosition());
 
     // Setting permitted state to "both" should not change an in-flight offset.
     verticalScroll(20.f);
     EXPECT_FLOAT_EQ(20, webView->topControls().contentOffset());
     webView->updateTopControlsState(WebTopControlsBoth, WebTopControlsBoth, false);
     EXPECT_FLOAT_EQ(20, webView->topControls().contentOffset());
+
+    // An animated state change shouldn't cause a change to the content offset
+    // since it'll be driven from the compositor.
+    webView->updateTopControlsState(WebTopControlsHidden, WebTopControlsHidden, true);
+    EXPECT_FLOAT_EQ(20, webView->topControls().contentOffset());
+
+    webView->updateTopControlsState(WebTopControlsShown, WebTopControlsShown, true);
+    EXPECT_FLOAT_EQ(20, webView->topControls().contentOffset());
+
+    // Setting just the constraint should affect the content offset.
+    webView->updateTopControlsState(WebTopControlsHidden, WebTopControlsBoth, false);
+    EXPECT_FLOAT_EQ(0, webView->topControls().contentOffset());
+
+    webView->updateTopControlsState(WebTopControlsShown, WebTopControlsBoth, false);
+    EXPECT_FLOAT_EQ(50, webView->topControls().contentOffset());
 }
 
 // Ensure that top controls do not affect the layout by showing and hiding
 // except for position: fixed elements.
 TEST_F(TopControlsTest, MAYBE(DontAffectLayoutHeight))
 {
     // Initialize with the top controls showing.
     WebViewImpl* webView = initialize("percent-height.html");
     webView->resizeWithTopControls(WebSize(400, 300), 100.f, true);
     webView->updateTopControlsState(
@@ skipping 238 matching lines @@
 
         ASSERT_EQ(80.f, webView->topControls().contentOffset());
         EXPECT_EQ(expectedRootOffset, rootViewport->scrollPosition().y());
 
         webView->handleInputEvent(
             generateEvent(WebInputEvent::GestureScrollEnd));
     }
 }
 
 } // namespace blink