Put Top Control resizing change behind a flag.

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 1775 matching lines @@
     page()->frameHost().visualViewport().setSize(newSize);
     page()->frameHost().visualViewport().clampToBoundaries();
 }
 
 void WebViewImpl::performResize()
 {
     // We'll keep the initial containing block size from changing when the top
     // controls hide so that the ICB will always be the same size as the
     // viewport with the top controls shown.
     IntSize ICBSize = m_size;
-    if (!topControls().shrinkViewport())
+    if (RuntimeEnabledFeatures::inertTopControlsEnabled() && !topControls().shrinkViewport())
         ICBSize.expand(0, -topControls().height());
 
     pageScaleConstraintsSet().didChangeInitialContainingBlockSize(ICBSize);
 
     updatePageDefinedViewportConstraints(mainFrameImpl()->frame()->document()->viewportDescription());
     updateMainFrameLayoutSize();
 
     page()->frameHost().visualViewport().setSize(m_size);
 
     if (mainFrameImpl()->frameView()) {
@@ skipping 2768 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