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

content/browser/renderer_host/render_widget_host_view_mac.mm

 // Copyright (c) 2012 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 "content/browser/renderer_host/render_widget_host_view_mac.h"
 
 #include <QuartzCore/QuartzCore.h>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 2254 matching lines @@
     // Note: All coordinates are in view units, not pixels.
     gfx::Rect bitmapRect(0, 0,
                          backingStore->size().width(),
                          backingStore->size().height());
 
     // Specify the proper y offset to ensure that the view is rooted to the
     // upper left corner.  This can be negative, if the window was resized
     // smaller and the renderer hasn't yet repainted.
     int yOffset = NSHeight([self bounds]) - backingStore->size().height();
 
-    gfx::Rect paintRect = bitmapRect.Intersect(damagedRect);
+    gfx::Rect paintRect = bitmapRect;
+    paintRect.Intersect(damagedRect);
     if (!paintRect.IsEmpty()) {
       // if we have a CGLayer, draw that into the window
       if (backingStore->cg_layer()) {
         CGContextRef context = static_cast<CGContextRef>(
             [[NSGraphicsContext currentContext] graphicsPort]);
 
         // TODO: add clipping to dirtyRect if it improves drawing performance.
         CGContextDrawLayerAtPoint(context, CGPointMake(0.0, yOffset),
                                   backingStore->cg_layer());
       } else {
@@ skipping 1014 matching lines @@
   if (!string) return NO;
 
   // If the user is currently using an IME, confirm the IME input,
   // and then insert the text from the service, the same as TextEdit and Safari.
   [self confirmComposition];
   [self insertText:string];
   return YES;
 }
 
 @end