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

third_party/WebKit/Source/web/WebViewImpl.cpp

 /*
  * Copyright (C) 2011, 2012 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 1813 matching lines @@
 
     if (mainFrameImpl()->frameView()) {
         if (!mainFrameImpl()->frameView()->needsLayout())
             postLayoutResize(mainFrameImpl());
     }
 }
 
 void WebViewImpl::updateTopControlsState(WebTopControlsState constraint, WebTopControlsState current, bool animate)
 {
     topControls().updateConstraints(constraint);
+
+    // If the change should be animated, let the impl thread drive the change.
+    // Otherwise, immediately set the shown ratio so we don't have to wait for
+    // a commit from the impl thread.
+    if (!animate) {
+        if (current == WebTopControlsShown)
+            topControls().setShownRatio(1.f);
+        else if (current == WebTopControlsHidden)
+            topControls().setShownRatio(0.f);

[majidvp, 2016/06/28 19:52:20]

Maybe it is worth it to specifically call out the TopControlsBoth case is a
no-op.
Perhaps this should become a switch statement instead?

[bokan, 2016/06/28 23:15:33]

Done.

+    }

[majidvp, 2016/06/28 19:52:20]

Why move the clamping logic out of top controls? I think this is internal logic
to TopControls and it is better to pass in animate boolean to the method
instead.

[bokan, 2016/06/28 23:15:33]

Done.

+
     if (m_layerTreeView)
         m_layerTreeView->updateTopControlsState(constraint, current, animate);
 }
 
 void WebViewImpl::didUpdateTopControls()
 {
     if (m_layerTreeView) {
         m_layerTreeView->setTopControlsShownRatio(topControls().shownRatio());
         m_layerTreeView->setTopControlsHeight(topControls().height(), topControls().shrinkViewport());
     }
@@ skipping 2677 matching lines @@
 {
     // TODO(oshima): Investigate if this should return the ScreenInfo's scale factor rather than
     // page's scale factor, which can be 1 in use-zoom-for-dsf mode.
     if (!page())
         return 1;
 
     return page()->deviceScaleFactor();
 }
 
 } // namespace blink