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

cc/delegated_renderer_layer_impl.cc

 // Copyright 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 "config.h"
 
 #include "CCDelegatedRendererLayerImpl.h"
 
 #include "CCAppendQuadsData.h"
 #include "cc/math_util.h"
@@ skipping 40 matching lines @@
     clearRenderPasses();
 
     for (size_t i = 0; i < renderPassesInDrawOrder.size(); ++i) {
         m_renderPassesIndexById.insert(std::pair<RenderPass::Id, int>(renderPassesInDrawOrder[i]->id(), i));
         m_renderPassesInDrawOrder.append(renderPassesInDrawOrder.take(i));
     }
     renderPassesInDrawOrder.clear();
 
     if (!m_renderPassesInDrawOrder.isEmpty()) {
         gfx::RectF newRootDamage = m_renderPassesInDrawOrder.last()->damageRect();
-        m_renderPassesInDrawOrder.last()->setDamageRect(oldRootDamage.Union(newRootDamage));
+        newRootDamage.Union(oldRootDamage);
+        m_renderPassesInDrawOrder.last()->setDamageRect(newRootDamage);
     }
 }
 
 void DelegatedRendererLayerImpl::clearRenderPasses()
 {
     // FIXME: Release the resources back to the nested compositor.
     m_renderPassesIndexById.clear();
     m_renderPassesInDrawOrder.clear();
 }
 
@@ skipping 104 matching lines @@
         quadSink.append(copyQuad.Pass(), appendQuadsData);
     }
 }
 
 const char* DelegatedRendererLayerImpl::layerTypeAsString() const
 {
     return "DelegatedRendererLayer";
 }
 
 }