change backing store cache to be memory-based rather than count

chrome/browser/renderer_host/backing_store_mac.cc

 // Copyright (c) 2006-2008 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"
 
 #include "base/logging.h"
 #include "chrome/common/transport_dib.h"
 #include "skia/ext/platform_canvas.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 
 BackingStore::BackingStore(RenderWidgetHost* widget, const gfx::Size& size)
     : render_widget_host_(widget),
       size_(size) {
   if (!canvas_.initialize(size.width(), size.height(), true))
     SK_CRASH();
 }
 
 BackingStore::~BackingStore() {
 }
 
+size_t BackingStore::MemorySize() {
+  // Always 4 bytes per pixel.
+  return size_.GetArea() * 4;
+}
+
 void BackingStore::PaintRect(base::ProcessHandle process,
                              TransportDIB* bitmap,
                              const gfx::Rect& bitmap_rect) {
   SkBitmap skbitmap;
   skbitmap.setConfig(SkBitmap::kARGB_8888_Config, bitmap_rect.width(),
                      bitmap_rect.height(), 4 * bitmap_rect.width());
 
   skbitmap.setPixels(bitmap->memory());
 
   canvas_.drawBitmap(skbitmap, bitmap_rect.x(), bitmap_rect.y());
@@ skipping 93 matching lines @@
         memcpy(x, x + stride * dy, len);
         x -= stride;
       }
     }
   }
 
   // Now paint the new bitmap data.
   PaintRect(process, bitmap, bitmap_rect);
   return;
 }