Don't ignore size updates that have a width and height == 0.

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 2840 matching lines @@
     updateLayerTreeViewport();
 
     // Relayout immediately to avoid violating the rule that needsLayout()
     // isn't set at the end of a layout.
     if (view->needsLayout())
         view->layout();
 }
 
 void WebViewImpl::updatePageDefinedViewportConstraints(const ViewportDescription& description)
 {
-    if (!settings()->viewportEnabled() || !page() || !m_size.width || !m_size.height)
+    if (!settings()->viewportEnabled() || !page() || (!m_size.width && !m_size.height))
         return;
 
     ViewportDescription adjustedDescription = description;
     if (settingsImpl()->viewportMetaLayoutSizeQuirk() && adjustedDescription.type == ViewportDescription::ViewportMeta) {
         if (adjustedDescription.maxWidth.type() == ExtendToZoom)
             adjustedDescription.maxWidth = Length(); // auto
         const int legacyWidthSnappingMagicNumber = 320;
         if (adjustedDescription.maxWidth.isFixed() && adjustedDescription.maxWidth.value() <= legacyWidthSnappingMagicNumber)
             adjustedDescription.maxWidth = Length(DeviceWidth);
         if (adjustedDescription.maxHeight.isFixed() && adjustedDescription.maxWidth.value() <= m_size.height)
@@ skipping 1113 matching lines @@
     const PageScaleConstraints& constraints = m_pageScaleConstraintsSet.pageDefinedConstraints();
 
     if (!mainFrameImpl() || !mainFrameImpl()->frameView())
         return false;
 
     return mainFrameImpl()->frameView()->layoutSize().width() == m_size.width
         || (constraints.minimumScale == constraints.maximumScale && constraints.minimumScale != -1);
 }
 
 } // namespace blink