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

Source/core/frame/FrameView.cpp

Index: Source/core/frame/FrameView.cpp
diff --git a/Source/core/frame/FrameView.cpp b/Source/core/frame/FrameView.cpp
index b2cb7359a68f53b55c55af84554c523b8af8c1e1..8d4e37669beac2a7711e85963dd0223d54e88026 100644
--- a/Source/core/frame/FrameView.cpp
+++ b/Source/core/frame/FrameView.cpp
@@ -3180,7 +3180,22 @@ void FrameView::setLayoutSizeInternal(const IntSize& 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, the next layout will do all the things required on layoutSize change.
+        // Otherwise we need to perform the post-layout tasks now.
+        if (!renderView->selfNeedsLayout()) {
+            // Call scheduleOrPerformPostLayoutTasks() instead of synchronized sendResizeEventIfNeeded()
+            // to avoid hang with resize events in seamless frames.

[esprehn, 2014/03/10 21:32:30]

We don't even have seamless anymore. This code seems suspect.

[Xianzhu, 2014/03/11 00:55:13]

Good news. Removed the comment.

Changed the code and added the comments after I encountered failure of a layout
test containing <iframe seamless> when I was preparing the first version of the
patch.

+            scheduleOrPerformPostLayoutTasks();
+            if (frame().page())
+                frame().page()->chrome().client().layoutUpdated(m_frame.get());
+        }
+    }
 }
 
 void FrameView::didAddScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)