Let synchronized painting generate correct paint invalidation rects

third_party/WebKit/Source/core/layout/LayoutBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index 15fa2e07ca658736df4a6257d6befc6bdf59c775..0e1b84882c9440623f265f9889a3e49940ab3afe 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -1430,18 +1430,30 @@ PaintInvalidationReason LayoutBox::invalidatePaintIfNeeded(PaintInvalidationStat
     // If we are set to do a full paint invalidation that means the LayoutView will be
     // issue paint invalidations. We can then skip issuing of paint invalidations for the child
     // layoutObjects as they'll be covered by the LayoutView.
-    if (!view()->doingFullPaintInvalidation() && !isFullPaintInvalidationReason(reason)) {
-        invalidatePaintForOverflowIfNeeded();
+    if (!view()->doingFullPaintInvalidation()) {
+        bool willDoFullInvalidation = isFullPaintInvalidationReason(reason);
+        if (!willDoFullInvalidation)
+            invalidatePaintForOverflowIfNeeded();
 
         // Issue paint invalidations for any scrollbars if there is a scrollable area for this layoutObject.
         if (ScrollableArea* area = scrollableArea()) {
             // In slimming paint mode, we already invalidated the display item clients of the scrollbars
             // during PaintLayerScrollableArea::invalidateScrollbarRect(). However, for now we still need to
             // invalidate the rectangles to trigger repaints.
-            if (area->hasVerticalBarDamage())
-                invalidatePaintRectangleNotInvalidatingDisplayItemClients(LayoutRect(area->verticalBarDamage()));
-            if (area->hasHorizontalBarDamage())
-                invalidatePaintRectangleNotInvalidatingDisplayItemClients(LayoutRect(area->horizontalBarDamage()));
+            if (area->hasVerticalBarDamage()) {
+                if (!willDoFullInvalidation)
+                    invalidatePaintRectangleNotInvalidatingDisplayItemClients(LayoutRect(area->verticalBarDamage()));
+                // TODO(wangxianzhu): Pass current bounds of the scrollbar to PaintController.
+                if (Scrollbar* verticalScrollbar = area->verticalScrollbar())
+                    invalidateDisplayItemClient(*verticalScrollbar);
+            }
+            if (area->hasHorizontalBarDamage()) {
+                if (!willDoFullInvalidation)
+                    invalidatePaintRectangleNotInvalidatingDisplayItemClients(LayoutRect(area->horizontalBarDamage()));
+                // TODO(wangxianzhu): Pass current bounds of the scrollbar to PaintController.
+                if (Scrollbar* horizontalScrollbar = area->horizontalScrollbar())
+                    invalidateDisplayItemClient(*horizontalScrollbar);
+            }
         }
     }