Root layer scrolling: set correct size for document's main GraphicsLayer.

third_party/WebKit/Source/core/frame/FrameView.cpp

Index: third_party/WebKit/Source/core/frame/FrameView.cpp
diff --git a/third_party/WebKit/Source/core/frame/FrameView.cpp b/third_party/WebKit/Source/core/frame/FrameView.cpp
index de49f4bed8fe9b65c1d2548956bca675c16783dc..e53c53f5c6359677dff739ebd0fded483f28fedb 100644
--- a/third_party/WebKit/Source/core/frame/FrameView.cpp
+++ b/third_party/WebKit/Source/core/frame/FrameView.cpp
@@ -1253,6 +1253,17 @@ void FrameView::removeViewportConstrainedObject(LayoutObject* object)
 
 void FrameView::viewportSizeChanged(bool widthChanged, bool heightChanged)
 {
+    if (m_frame->settings() && m_frame->settings()->rootLayerScrolls()) {
+        // The background must be repainted when the FrameView is resized, even if the initial
+        // containing block does not change (so we can't rely on layout to issue the invalidation).
+        // This is because the background fills the main GraphicsLayer, which takes the size of the
+        // layout viewport.
+        // TODO(skobes): Paint non-fixed backgrounds into the scrolling contents layer and avoid
+        // this invalidation (http://crbug.com/568847).
+        if (LayoutView* lv = layoutView())
+            lv->setShouldDoFullPaintInvalidation();
+    }
+
     if (!hasViewportConstrainedObjects())
         return;