Optimize scroll adjustment for paint invalidation

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

 // Copyright 2016 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 "core/paint/ObjectPaintInvalidator.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/LocalFrame.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/api/LayoutPartItem.h"
@@ skipping 387 matching lines @@
 
   if (m_object.view()->document().printing() &&
       !RuntimeEnabledFeatures::printBrowserEnabled())
     return LayoutRect();  // Don't invalidate paints if we're printing.
 
   const LayoutBoxModelObject& paintInvalidationContainer =
       m_object.containerForPaintInvalidation();
   LayoutRect dirtyRectOnBacking = dirtyRect;
   PaintLayer::mapRectToPaintInvalidationBacking(
       m_object, paintInvalidationContainer, dirtyRectOnBacking);
-  dirtyRectOnBacking.move(m_object.scrollAdjustmentForPaintInvalidation(
-      paintInvalidationContainer));
+  if (m_object != paintInvalidationContainer) {
+    dirtyRectOnBacking.move(
+        paintInvalidationContainer.scrollAdjustmentForPaintInvalidation());
+  }
   invalidatePaintUsingContainer(paintInvalidationContainer, dirtyRectOnBacking,
                                 PaintInvalidationRectangle);
 
   slowSetPaintingLayerNeedsRepaint();
   if (displayItemClient)
     invalidateDisplayItemClient(*displayItemClient, PaintInvalidationRectangle);
   else
     m_object.invalidateDisplayItemClients(PaintInvalidationRectangle);
 
   return dirtyRectOnBacking;
@@ skipping 226 matching lines @@
 
   m_context.paintingLayer->setNeedsRepaint();
   m_object.invalidateDisplayItemClients(reason);
   return reason;
 }
 
 DisablePaintInvalidationStateAsserts::DisablePaintInvalidationStateAsserts()
     : m_disabler(&gDisablePaintInvalidationStateAsserts, true) {}
 
 }  // namespace blink