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

ui/app_list/views/cached_label.cc

+// Copyright (c) 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() {
+  if (bitmap_.width() != width() || bitmap_.height() != height()) {
+    bitmap_.setConfig(SkBitmap::kARGB_8888_Config, width(), height());
+    bitmap_.allocPixels();
+    image_ = gfx::ImageSkia::CreateFrom1xBitmap(bitmap_);
+  }
+
+  SkCanvas sk_canvas(bitmap_);
+  scoped_ptr<gfx::Canvas> canvas(gfx::Canvas::CreateCanvasWithoutScaling(
+      &sk_canvas, ui::SCALE_FACTOR_100P));
+
+  canvas->FillRect(gfx::Rect(0, 0, width(), height()),
+                   SkColorSetARGB(0x0, 0, 0, 0), SkXfermode::kSrc_Mode);
+  Label::OnPaint(canvas.get());
+}
+
+void CachedLabel::OnPaint(gfx::Canvas* canvas) {
+  if (needs_repaint_)
+    PaintToBackingImage();
+  needs_repaint_ = false;
+  canvas->DrawImageInt(image_, 0, 0);
+}
+
+}  // namespace app_list