Recalc styles on resize if we have viewport units.

Source/WebCore/page/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 1090 matching lines @@
             m_inSynchronousPostLayout = true;
             performPostLayoutTasks();
             m_inSynchronousPostLayout = false;
         }
 
         // Viewport-dependent media queries may cause us to need completely different style information.
         // Check that here.
         if (document->styleResolver()->affectedByViewportChange()) {
             document->styleResolverChanged(RecalcStyleImmediately);
             InspectorInstrumentation::mediaQueryResultChanged(document);
-        } else
+        } else {
             document->evaluateMediaQueryList();
+            if (document->styleSheetCollection()->usesViewportUnits()) {
+                document->styleResolver()->invalidateMatchedPropertiesCache();
+                document->scheduleForcedStyleRecalc();

[esprehn, 2013/04/09 08:20:27]

This is a big hammer. It's going to mean pretty crushing performance if you have
a big page with viewport units and resize it. ex. resizing the HTML5 spec window
if it used even a single vh or vw unit.

+            }
+        }
 
         // If there is any pagination to apply, it will affect the RenderView's style, so we should
         // take care of that now.
         applyPaginationToViewport();
 
         // Always ensure our style info is up-to-date. This can happen in situations where
-        // the layout beats any sort of style recalc update that needs to occur.
+        // the layout beats any sort of style recalc update that needs to occur, and if we

[esprehn, 2013/04/09 08:20:27]

"or if" is probably more clear. I had to read this a few times to understand.

+        // have to recalc due to the presence of viewport units.
         TemporaryChange<bool> changeDoingPreLayoutStyleUpdate(m_doingPreLayoutStyleUpdate, true);
         document->updateStyleIfNeeded();
 
         subtree = m_layoutRoot;
 
         // If there is only one ref to this view left, then its going to be destroyed as soon as we exit, 
         // so there's no point to continuing to layout
         if (protector->hasOneRef())
             return;
 
@@ skipping 2692 matching lines @@
     if (frame() && frame()->document())
         return frame()->document()->existingAXObjectCache();
     return 0;
 }
     
 void FrameView::setScrollingPerformanceLoggingEnabled(bool)
 {
 }
 
 } // namespace WebCore