Recalc styles on resize if we have viewport units.

Source/WebCore/page/FrameView.cpp

Index: Source/WebCore/page/FrameView.cpp
diff --git a/Source/WebCore/page/FrameView.cpp b/Source/WebCore/page/FrameView.cpp
index 3fe41c9ffec46ee4cabe8e6434496e3fc28d83cb..d9f10b718ed40649f1d8deef663c567bb8ff84b8 100644
--- a/Source/WebCore/page/FrameView.cpp
+++ b/Source/WebCore/page/FrameView.cpp
@@ -1108,15 +1108,21 @@ void FrameView::layout(bool allowSubtree)
         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();