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

ash/drag_drop/drag_drop_controller_unittest.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 "ash/drag_drop/drag_drop_controller.h"
 
 #include "ash/shell.h"
 #include "ash/test/ash_test_base.h"
 #include "base/location.h"
 #include "base/utf_string_conversions.h"
@@ skipping 189 matching lines @@
 void AddViewToWidgetAndResize(views::Widget* widget, views::View* view) {
   if (!widget->GetContentsView()) {
     views::View* contents_view = new views::View;
     widget->SetContentsView(contents_view);
   }
 
   views::View* contents_view = widget->GetContentsView();
   contents_view->AddChildView(view);
   view->SetBounds(contents_view->width(), 0, 100, 100);
   gfx::Rect contents_view_bounds = contents_view->bounds();
-  contents_view_bounds = contents_view_bounds.Union(view->bounds());
+  contents_view_bounds.Union(view->bounds());
   contents_view->SetBoundsRect(contents_view_bounds);
   widget->SetBounds(contents_view_bounds);
 }
 
 }  // namespace
 
 class DragDropControllerTest : public AshTestBase {
  public:
   DragDropControllerTest() : AshTestBase() {}
   virtual ~DragDropControllerTest() {}
@@ skipping 446 matching lines @@
   EXPECT_EQ(1, drag_view->num_drag_enters_);
   EXPECT_EQ(num_drags - 1 - drag_view->VerticalDragThreshold(),
       drag_view->num_drag_updates_);
   EXPECT_EQ(0, drag_view->num_drops_);
   EXPECT_EQ(1, drag_view->num_drag_exits_);
   EXPECT_TRUE(drag_view->drag_done_received_);
 }
 
 }  // namespace test
 }  // namespace aura