cc: Don't use partial updates for scrollbars when they are not allowed.

cc/test/fake_scrollbar_layer.h

+// 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 CC_TEST_FAKE_SCROLLBAR_LAYER_H_
+#define CC_TEST_FAKE_SCROLLBAR_LAYER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "cc/scrollbar_layer.h"
+
+namespace cc {
+
+class FakeScrollbarLayer : public ScrollbarLayer {
+public:
+  static scoped_refptr<FakeScrollbarLayer> Create(
+      bool paint_during_update, int scrolling_layer_id) {
+    return make_scoped_refptr(new FakeScrollbarLayer(
+        paint_during_update, scrolling_layer_id)); 
+  }
+
+  int update_count() { return update_count_; }
+  void reset_update_count() { update_count_ = 0; }
+
+  virtual void update(
+      ResourceUpdateQueue& queue,
+      const OcclusionTracker* occlusion,
+      RenderingStats& stats) OVERRIDE;
+
+private:
+  FakeScrollbarLayer(bool paint_during_update, int scrolling_layer_id);
+  virtual ~FakeScrollbarLayer();
+
+  int update_count_;
+};
+
+}  // namespace cc
+
+#endif  // CC_TEST_FAKE_SCROLLBAR_LAYER_H_