Move core pieces of browser\renderer_host to src\content.

chrome/browser/renderer_host/backing_store.cc

-// Copyright (c) 2010 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 "chrome/browser/renderer_host/backing_store.h"
-
-BackingStore::BackingStore(RenderWidgetHost* widget, const gfx::Size& size)
-    : render_widget_host_(widget),
-      size_(size) {
-}
-
-BackingStore::~BackingStore() {
-}
-
-size_t BackingStore::MemorySize() {
-  return size_.GetArea() * 4;
-}