Efficiently handle image layer scaling

cc/picture_image_layer.cc

Index: cc/picture_image_layer.cc
diff --git a/cc/picture_image_layer.cc b/cc/picture_image_layer.cc
index 14864464ae12dc50ddc9d5e202e23c15dd08c3ba..0fb908f956f33cd47281f9d68493842c97edcbbc 100644
--- a/cc/picture_image_layer.cc
+++ b/cc/picture_image_layer.cc
@@ -4,6 +4,7 @@
 
 #include "cc/picture_image_layer.h"
 
+#include "cc/picture_image_layer_impl.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 
 namespace cc {
@@ -23,6 +24,15 @@ PictureImageLayer::~PictureImageLayer()
   clearClient();
 }
 
+scoped_ptr<LayerImpl> PictureImageLayer::createLayerImpl(
+    LayerTreeImpl* treeImpl) {
+  return PictureImageLayerImpl::create(treeImpl, id()).PassAs<LayerImpl>();
+}
+
+bool PictureImageLayer::drawsContent() const {
+  return !bitmap_.isNull() && PictureLayer::drawsContent();
+}
+
 void PictureImageLayer::setBitmap(const SkBitmap& bitmap)
 {
   // setBitmap() currently gets called whenever there is any
@@ -36,21 +46,6 @@ void PictureImageLayer::setBitmap(const SkBitmap& bitmap)
   setNeedsDisplay();
 }
 
-void PictureImageLayer::update(
-    ResourceUpdateQueue& queue,
-    const OcclusionTracker* tracker,
-    RenderingStats* stats) {
-  if (bounds() != bounds_) {
-    // Pictures are recorded in layer space, so if the layer size changes,
-    // then the picture needs to be re-scaled, as a directly composited image
-    // always fills its entire layer bounds.  This could be improved by
-    // recording pictures of images at their actual resolution somehow.
-    bounds_ = bounds();
-    setNeedsDisplay();
-  }
-  PictureLayer::update(queue, tracker, stats);
-}
-
 void PictureImageLayer::paintContents(
     SkCanvas* canvas,
     const gfx::Rect& clip,
@@ -58,11 +53,10 @@ void PictureImageLayer::paintContents(
   if (!bitmap_.width() || !bitmap_.height())
     return;
 
-  SkScalar content_to_layer_scale_x = SkFloatToScalar(
-      static_cast<float>(bounds().width()) / bitmap_.width());
-  SkScalar content_to_layer_scale_y = SkFloatToScalar(
-      static_cast<float>(bounds().height()) / bitmap_.height());
-  canvas->scale(content_to_layer_scale_x, content_to_layer_scale_y);
+  // WebImageLayerImpl should always set bounds equaling to the size of the
+  // bitmap.
+  DCHECK(bounds().width() == bitmap_.width() &&
+         bounds().height() == bitmap_.height());
 
   canvas->drawBitmap(bitmap_, 0, 0);
 }