Efficiently handle image layer scaling

cc/picture_image_layer_impl.cc

Index: cc/picture_image_layer_impl.cc
diff --git a/cc/picture_image_layer_impl.cc b/cc/picture_image_layer_impl.cc
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index 0000000000000000000000000000000000000000..806670212d22c97592b8ea874229c8c843a9c071
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+++ b/cc/picture_image_layer_impl.cc
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+// 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 "cc/picture_image_layer_impl.h"
+
+#include "cc/debug_colors.h"
+#include "cc/layer_tree_impl.h"
+
+namespace cc {
+
+PictureImageLayerImpl::PictureImageLayerImpl(LayerTreeImpl* treeImpl, int id)
+    : PictureLayerImpl(treeImpl, id) {
+}
+
+PictureImageLayerImpl::~PictureImageLayerImpl() {
+}
+
+const char* PictureImageLayerImpl::layerTypeAsString() const {
+  return "PictureImageLayer";
+}
+
+scoped_ptr<LayerImpl> PictureImageLayerImpl::createLayerImpl(
+    LayerTreeImpl* treeImpl) {
+  return PictureImageLayerImpl::create(treeImpl, id()).PassAs<LayerImpl>();
+}
+
+void PictureImageLayerImpl::getDebugBorderProperties(
+    SkColor* color, float* width) const {
+  *color = DebugColors::ImageLayerBorderColor();
+  *width = DebugColors::ImageLayerBorderWidth(layerTreeImpl());
+}
+
+void PictureImageLayerImpl::CalculateRasterContentsScale(
+    bool animating_transform_to_screen,
+    float* raster_contents_scale,
+    float* low_res_raster_contents_scale) {
+  // Don't scale images during rastering to ensure image quality, save memory
+  // and avoid frequent re-rastering on change of scale.
+  *raster_contents_scale =
+      std::max(1.f, layerTreeImpl()->settings().minimumContentsScale);
+  // We don't need low res tiles.
+  *low_res_raster_contents_scale = *raster_contents_scale;
+}
+
+}  // namespace cc