Make painting app list items more efficient by caching the labels.

ui/app_list/views/cached_label.h

+// Copyright 2013 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 UI_APP_LIST_VIEWS_CACHED_LABEL_H_
+#define UI_APP_LIST_VIEWS_CACHED_LABEL_H_
+
+#include "ui/gfx/image/image_skia.h"
+#include "ui/views/controls/label.h"
+#include "ui/views/view.h"
+
+namespace gfx {
+class Canvas;
+}
+
+namespace app_list {
+
+// Subclass of views::Label that caches the rendered text in an ImageSkia.
+class CachedLabel : public views::Label {
+ public:
+  CachedLabel();
+
+  // Have the next call to OnPaint() update the backing image.
+  void Invalidate() { needs_repaint_ = true; }
+
+#if defined(OS_WIN)
+  // views::View overrides.
+  virtual void OnPaint(gfx::Canvas* canvas) OVERRIDE;
+#endif
+
+ private:
+  // Calls the base label's OnPaint() to paint into a backing image.
+  void PaintToBackingImage();
+
+  bool needs_repaint_;
+  gfx::ImageSkia image_;
+};
+
+}  // namespace app_list
+
+#endif  // UI_APP_LIST_VIEWS_CACHED_LABEL_H_