Make gfx::Rect class operations consistently mutate the class they are called on.

ppapi/utility/graphics/paint_aggregator.cc

 // Copyright (c) 2011 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 "ppapi/utility/graphics/paint_aggregator.h"
 
 #include <algorithm>
 
 #include "ppapi/cpp/logging.h"
 
@@ skipping 189 matching lines @@
   // an invalidation of the scroll.
   if (ShouldInvalidateScrollRect(Rect()))
     InvalidateScrollRect();
 }
 
 Rect PaintAggregator::ScrollPaintRect(const Rect& paint_rect,
                                       const Point& amount) const {
   Rect result = paint_rect;
 
   result.Offset(amount);
-  result = update_.scroll_rect.Intersect(result);
+  result.Intersect(update_.scroll_rect);
 
   // Subtract out the scroll damage rect to avoid redundant painting.
   return result.Subtract(update_.GetScrollDamage());
 }
 
 bool PaintAggregator::ShouldInvalidateScrollRect(const Rect& rect) const {
   if (!rect.IsEmpty()) {
     if (!update_.scroll_rect.Intersects(rect))
       return false;
 
@@ skipping 49 matching lines @@
         outer = outer.Union(existing_rect);
       }
     }
     update_.paint_rects.clear();
     update_.paint_rects.push_back(inner);
     update_.paint_rects.push_back(outer);
   }
 }
 
 }  // namespace pp