Reduce texture uploads during scrollbar invalidations.

cc/caching_bitmap_canvas_layer_texture_updater.h

Index: cc/caching_bitmap_canvas_layer_texture_updater.h
diff --git a/cc/caching_bitmap_canvas_layer_texture_updater.h b/cc/caching_bitmap_canvas_layer_texture_updater.h
new file mode 100644
index 0000000000000000000000000000000000000000..6b10dd8975a60c2efef053e8c3a1a86ef6209d01
--- /dev/null
+++ b/cc/caching_bitmap_canvas_layer_texture_updater.h
@@ -0,0 +1,38 @@
+// 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.
+
+#ifndef CACHING_BITMAP_CANVAS_LAYER_TEXTURE_UPDATER_H_
+#define CACHING_BITMAP_CANVAS_LAYER_TEXTURE_UPDATER_H_
+
+#include "base/compiler_specific.h"
+#include "BitmapCanvasLayerTextureUpdater.h"
+
+namespace cc {
+
+class CachingBitmapCanvasLayerTextureUpdater
+    : public BitmapCanvasLayerTextureUpdater {
+ public:
+  static PassRefPtr<CachingBitmapCanvasLayerTextureUpdater> Create(
+      PassOwnPtr<LayerPainterChromium>);
+
+  virtual void prepareToUpdate(const IntRect& content_rect,
+                               const IntSize& tile_size,
+                               float contents_width_scale,
+                               float contents_height_scale,
+                               IntRect& resulting_opaque_rect,
+                               CCRenderingStats&) OVERRIDE;
+
+  bool PixelsDidChange() { return pixels_did_change_; }
+
+ private:
+  CachingBitmapCanvasLayerTextureUpdater(
+      PassOwnPtr<LayerPainterChromium> painter);
+
+  bool pixels_did_change_;
+  uint32 pixel_hash_;
+};
+
+}  // namespace cc
+
+#endif  // CACHINGBITMAPCANVASLAYERTEXTUREUPDATER_H_