Add non-member non-mutating methods for common gfx::Rect operations.

ash/wm/partial_screenshot_view.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/wm/partial_screenshot_view.h"
 
 #include "ash/screenshot_delegate.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
 #include "ash/wm/overlay_event_filter.h"
@@ skipping 103 matching lines @@
 }
 
 void PartialScreenshotView::OnMouseReleased(const ui::MouseEvent& event) {
   Cancel();
   if (!is_dragging_)
     return;
 
   is_dragging_ = false;
   if (screenshot_delegate_) {
     aura::RootWindow *root_window = Shell::GetPrimaryRootWindow();
-    gfx::Rect root_window_screenshot_rect = root_window->bounds();
-    root_window_screenshot_rect.Intersect(GetScreenshotRect());
     screenshot_delegate_->HandleTakePartialScreenshot(
-        root_window, root_window_screenshot_rect);
+        root_window,
+        gfx::IntersectRects(root_window->bounds(), GetScreenshotRect()));
   }
 }
 
 gfx::Rect PartialScreenshotView::GetScreenshotRect() const {
   int left = std::min(start_position_.x(), current_position_.x());
   int top = std::min(start_position_.y(), current_position_.y());
   int width = ::abs(start_position_.x() - current_position_.x());
   int height = ::abs(start_position_.y() - current_position_.y());
   return gfx::Rect(left, top, width, height);
 }
 
 }  // namespace ash