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

ppapi/utility/graphics/paint_manager.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 "ppapi/utility/graphics/paint_manager.h"
 
 #include "ppapi/c/pp_errors.h"
 #include "ppapi/cpp/instance.h"
 #include "ppapi/cpp/logging.h"
 #include "ppapi/cpp/module.h"
@@ skipping 59 matching lines @@
 
   EnsureCallbackPending();
   aggregator_.InvalidateRect(Rect(GetEffectiveSize()));
 }
 
 void PaintManager::InvalidateRect(const Rect& rect) {
   // You must call SetSize before using.
   PP_DCHECK(!graphics_.is_null() || has_pending_resize_);
 
   // Clip the rect to the device area.
-  Rect clipped_rect = rect.Intersect(Rect(GetEffectiveSize()));
+  Rect clipped_rect = rect;
+  clipped_rect.Intersect(Rect(GetEffectiveSize()));
   if (clipped_rect.IsEmpty())
     return;  // Nothing to do.
 
   EnsureCallbackPending();
   aggregator_.InvalidateRect(clipped_rect);
 }
 
 void PaintManager::ScrollRect(const Rect& clip_rect, const Point& amount) {
   // You must call SetSize before using.
   PP_DCHECK(!graphics_.is_null() || has_pending_resize_);
@@ skipping 109 matching lines @@
   // Just because we have a manual callback doesn't mean there are actually any
   // invalid regions. Even though we only schedule this callback when something
   // is pending, a Flush callback could have come in before this callback was
   // executed and that could have cleared the queue.
   if (aggregator_.HasPendingUpdate() && !flush_pending_)
     DoPaint();
 }
 
 
 }  // namespace pp