Put Top Control resizing change behind a flag.

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 1119 matching lines @@
             return IntRect();
 
         us.intersect(parentRect);
     }
 
     return us;
 }
 
 FloatSize FrameView::viewportSizeForViewportUnits() const
 {
+    float zoom = frame().pageZoomFactor();
+
+    if (m_frame->settings() && !RuntimeEnabledFeatures::inertTopControlsEnabled()) {
+        FloatSize viewportSize;
+
+        LayoutView* layoutView = this->layoutView();
+        if (!layoutView)
+            return viewportSize;
+
+        viewportSize.setWidth(layoutView->viewWidth(IncludeScrollbars) / zoom);
+        viewportSize.setHeight(layoutView->viewHeight(IncludeScrollbars) / zoom);
+        return viewportSize;
+    }
+
     FloatSize size(layoutSize(IncludeScrollbars));
 
     // We use the layoutSize rather than frameRect to calculate viewport units
     // so that we get correct results on mobile where the page is laid out into
     // a rect that may be larger than the viewport (e.g. the 980px fallback
     // width for desktop pages). Since the layout height is statically set to
     // be the viewport with top controls showing, we add the top controls
     // height, compensating for page scale as well, since we want to use the
     // viewport with top controls hidden for vh (to match Safari).
     TopControls& topControls = m_frame->host()->topControls();
     if (m_frame->isMainFrame() && size.width()) {
         float pageScaleAtLayoutWidth =
             m_frame->host()->visualViewport().size().width() / size.width();
         size.expand(0, topControls.height() / pageScaleAtLayoutWidth);
     }
 
-    float scale = frame().pageZoomFactor();
-    size.scale(1 / scale);
+    size.scale(1 / zoom);
     return size;
 }
 
 DocumentLifecycle& FrameView::lifecycle() const
 {
     return m_frame->document()->lifecycle();
 }
 
 LayoutBox* FrameView::embeddedContentBox() const
 {
@@ skipping 2945 matching lines @@
     return m_hiddenForThrottling && m_crossOriginForThrottling;
 }
 
 LayoutBox& FrameView::boxForScrollControlPaintInvalidation() const
 {
     ASSERT(layoutView());
     return *layoutView();
 }
 
 } // namespace blink