Revert 148647 "Remove frame flattening support as Chromium has n..."

trunk/Source/core/platform/ScrollView.cpp

Index: trunk/Source/core/platform/ScrollView.cpp
===================================================================
--- trunk/Source/core/platform/ScrollView.cpp	(revision 148648)
+++ trunk/Source/core/platform/ScrollView.cpp	(working copy)
@@ -82,7 +82,7 @@
 
 void ScrollView::setHasHorizontalScrollbar(bool hasBar)
 {
-    ASSERT(!hasBar);
+    ASSERT(!hasBar || !avoidScrollbarCreation());
     if (hasBar && !m_horizontalScrollbar) {
         m_horizontalScrollbar = createScrollbar(HorizontalScrollbar);
         addChild(m_horizontalScrollbar.get());
@@ -93,14 +93,14 @@
         removeChild(m_horizontalScrollbar.get());
         m_horizontalScrollbar = 0;
     }
-
+    
     if (AXObjectCache* cache = axObjectCache())
         cache->handleScrollbarUpdate(this);
 }
 
 void ScrollView::setHasVerticalScrollbar(bool hasBar)
 {
-    ASSERT(!hasBar);
+    ASSERT(!hasBar || !avoidScrollbarCreation());
     if (hasBar && !m_verticalScrollbar) {
         m_verticalScrollbar = createScrollbar(VerticalScrollbar);
         addChild(m_verticalScrollbar.get());
@@ -425,13 +425,13 @@
         newHasVerticalScrollbar = (vScroll == ScrollbarAlwaysOn);
 
     if (m_scrollbarsSuppressed || (hScroll != ScrollbarAuto && vScroll != ScrollbarAuto)) {
-        if (hasHorizontalScrollbar != newHasHorizontalScrollbar && hasHorizontalScrollbar)
+        if (hasHorizontalScrollbar != newHasHorizontalScrollbar && (hasHorizontalScrollbar || !avoidScrollbarCreation()))
             setHasHorizontalScrollbar(newHasHorizontalScrollbar);
-        if (hasVerticalScrollbar != newHasVerticalScrollbar && hasVerticalScrollbar)
+        if (hasVerticalScrollbar != newHasVerticalScrollbar && (hasVerticalScrollbar || !avoidScrollbarCreation()))
             setHasVerticalScrollbar(newHasVerticalScrollbar);
     } else {
         bool sendContentResizedNotification = false;
-
+        
         IntSize docSize = totalContentsSize();
         IntSize fullVisibleSize = visibleContentRect(IncludeScrollbars).size();
 
@@ -454,7 +454,7 @@
             newHasHorizontalScrollbar = false;
 
         bool scrollbarIsOverlay = ScrollbarTheme::theme()->usesOverlayScrollbars();
-        if (hasHorizontalScrollbar != newHasHorizontalScrollbar && hasHorizontalScrollbar) {
+        if (hasHorizontalScrollbar != newHasHorizontalScrollbar && (hasHorizontalScrollbar || !avoidScrollbarCreation())) {
             if (!scrollbarIsOverlay)
                 sendContentResizedNotification = true;
             if (scrollOrigin().y() && !newHasHorizontalScrollbar && !scrollbarIsOverlay)
@@ -464,7 +464,7 @@
             setHasHorizontalScrollbar(newHasHorizontalScrollbar);
         }
 
-        if (hasVerticalScrollbar != newHasVerticalScrollbar && hasVerticalScrollbar) {
+        if (hasVerticalScrollbar != newHasVerticalScrollbar && (hasVerticalScrollbar || !avoidScrollbarCreation())) {
             if (!scrollbarIsOverlay)
                 sendContentResizedNotification = true;
             if (scrollOrigin().x() && !newHasVerticalScrollbar && !scrollbarIsOverlay)