Change Widget subclasses to use a CullRect instead of an IntRect for painting.

third_party/WebKit/Source/core/paint/PartPainter.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/paint/PartPainter.h"
 
 #include "core/layout/LayoutPart.h"
 #include "core/paint/BoxPainter.h"
 #include "core/paint/LayoutObjectDrawingRecorder.h"
@@ skipping 89 matching lines @@
     LayoutPoint adjustedPaintOffset = paintOffset + m_layoutPart.location();
 
     Widget* widget = m_layoutPart.widget();
     RELEASE_ASSERT(widget);
 
     // Tell the widget to paint now. This is the only time the widget is allowed
     // to paint itself. That way it will composite properly with z-indexed layers.
     IntPoint widgetLocation = widget->frameRect().location();
     IntPoint paintLocation(roundToInt(adjustedPaintOffset.x() + m_layoutPart.borderLeft() + m_layoutPart.paddingLeft()),
         roundToInt(adjustedPaintOffset.y() + m_layoutPart.borderTop() + m_layoutPart.paddingTop()));
-    IntRect paintRect = paintInfo.cullRect().m_rect;
 
     IntSize widgetPaintOffset = paintLocation - widgetLocation;
     // When painting widgets into compositing layers, tx and ty are relative to the enclosing compositing layer,
-    // not the root. In this case, shift the CTM and adjust the paintRect to be root-relative to fix plugin drawing.
+    // not the root. In this case, shift the CTM and adjust the CullRect to be root-relative to fix plugin drawing.
     TransformRecorder transform(*paintInfo.context, m_layoutPart,
         AffineTransform::translation(widgetPaintOffset.width(), widgetPaintOffset.height()));
-    paintRect.move(-widgetPaintOffset);
-    widget->paint(paintInfo.context, paintRect);
+
+    CullRect adjustedCullRect(paintInfo.cullRect(), -widgetPaintOffset);
+    widget->paint(paintInfo.context, adjustedCullRect);
 }
 
 } // namespace blink