Avoid layout/full-repaint on view height change if possible

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 3474 matching lines @@
 
     ScrollView::frameRectsChanged();
 }
 
 void FrameView::setLayoutSizeInternal(const IntSize& size)
 {
     if (m_layoutSize == size)
         return;
 
     m_layoutSize = size;
-    contentsResized();
+
+    // Update scrollbars. Not calling this->contentsResized() to avoid setNeedsLayout.
+    ScrollView::contentsResized();
+
+    if (RenderView* renderView = this->renderView()) {
+        renderView->viewResized();
+        // If selfNeedsLayout, resize event will be sent if needed during the next layout;
+        // otherwise we need to send the resize event now if needed.
+        if (!renderView->selfNeedsLayout()) {
+            // Call scheduleOrPerformPostLayoutTasks() instead of synchronized sendResizeEventIfNeeded()
+            // to avoid hang with resize events in seamless frames.
+            scheduleOrPerformPostLayoutTasks();
+        }
+    }
 }
 
 void FrameView::didAddScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)
 {
     ScrollableArea::didAddScrollbar(scrollbar, orientation);
     if (AXObjectCache* cache = axObjectCache())
         cache->handleScrollbarUpdate(this);
 }
 
 void FrameView::willRemoveScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)
 {
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
     if (AXObjectCache* cache = axObjectCache()) {
         cache->remove(scrollbar);
         cache->handleScrollbarUpdate(this);
     }
 }
 
 } // namespace WebCore