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

content/plugin/webplugin_proxy.cc

 // 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/plugin/webplugin_proxy.h"
 
 #include "build/build_config.h"
 
 #include "base/bind.h"
 #include "base/lazy_instance.h"
@@ skipping 161 matching lines @@
   }
 
   // Some plugins will send invalidates larger than their own rect when
   // offscreen, so constrain invalidates to the plugin rect.
   gfx::Rect plugin_rect = delegate_->GetRect();
   plugin_rect.set_origin(gfx::Point(0, 0));
   const gfx::Rect invalidate_rect(rect.Intersect(plugin_rect));
 #else
   const gfx::Rect invalidate_rect(rect);
 #endif
-  damaged_rect_ = damaged_rect_.Union(invalidate_rect);
+  damaged_rect_.Union(invalidate_rect);
   // Ignore NPN_InvalidateRect calls with empty rects.  Also don't send an
   // invalidate if it's outside the clipping region, since if we did it won't
   // lead to a paint and we'll be stuck waiting forever for a DidPaint response.
   //
   // TODO(piman): There is a race condition here, because this test assumes
   // that when the paint actually occurs, the clip rect will not have changed.
   // This is not true because scrolling (or window resize) could occur and be
   // handled by the renderer before it receives the InvalidateRect message,
   // changing the clip rect and then not painting.
   if (damaged_rect_.IsEmpty() ||
@@ skipping 586 matching lines @@
   // Retrieve the IME status from a plug-in and send it to a renderer process
   // when the plug-in has updated it.
   int input_type;
   gfx::Rect caret_rect;
   if (!delegate_->GetIMEStatus(&input_type, &caret_rect))
     return;
 
   Send(new PluginHostMsg_NotifyIMEStatus(route_id_, input_type, caret_rect));
 }
 #endif