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

ui/app_list/views/cached_label.cc

+// 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.
+
+#include "ui/app_list/views/cached_label.h"
+
+#include "base/utf_string_conversions.h"
+#include "ui/base/resource/resource_bundle.h"
+#include "ui/gfx/canvas.h"
+
+namespace app_list {
+
+CachedLabel::CachedLabel()
+    : needs_repaint_(true) {
+}
+
+void CachedLabel::PaintToBackingImage() {
+  gfx::Canvas canvas(size(), ui::SCALE_FACTOR_100P, false /* is_opaque */);
+  canvas.FillRect(GetLocalBounds(), SkColorSetARGB(0, 0, 0, 0),
+                  SkXfermode::kSrc_Mode);
+  Label::OnPaint(&canvas);
+  image_ = gfx::ImageSkia(canvas.ExtractImageRep());
+}
+
+#if defined(OS_WIN)
+void CachedLabel::OnPaint(gfx::Canvas* canvas) {
+  if (needs_repaint_)
+    PaintToBackingImage();
+  needs_repaint_ = false;
+  canvas->DrawImageInt(image_, 0, 0);
+}
+#endif
+
+}  // namespace app_list