Skip clearing the canvas before painting the contents of opaque layers

cc/resources/bitmap_content_layer_updater.cc

Index: cc/resources/bitmap_content_layer_updater.cc
diff --git a/cc/resources/bitmap_content_layer_updater.cc b/cc/resources/bitmap_content_layer_updater.cc
index 3d90eb0a4d566fbf82dbf258452021230f6fd46f..75b99c54b81fedb7dfe94355634acbc05706002a 100644
--- a/cc/resources/bitmap_content_layer_updater.cc
+++ b/cc/resources/bitmap_content_layer_updater.cc
@@ -43,8 +43,7 @@ BitmapContentLayerUpdater::BitmapContentLayerUpdater(
     scoped_ptr<LayerPainter> painter,
     RenderingStatsInstrumentation* stats_instrumentation,
     int layer_id)
-    : ContentLayerUpdater(painter.Pass(), stats_instrumentation, layer_id),
-      opaque_(false) {}
+    : ContentLayerUpdater(painter.Pass(), stats_instrumentation, layer_id) {}
 
 BitmapContentLayerUpdater::~BitmapContentLayerUpdater() {}
 
@@ -67,13 +66,13 @@ void BitmapContentLayerUpdater::PrepareToUpdate(
         devtools_instrumentation::kPaintSetup, layer_id_);
     canvas_size_ = content_rect.size();
     canvas_ = skia::AdoptRef(skia::CreateBitmapCanvas(
-        canvas_size_.width(), canvas_size_.height(), opaque_));
+        canvas_size_.width(), canvas_size_.height(), layer_is_opaque_));
   }
 
   base::TimeTicks start_time =
       rendering_stats_instrumentation_->StartRecording();
   PaintContents(canvas_.get(),
-                content_rect,
+                content_rect.origin(),
                 contents_width_scale,
                 contents_height_scale,
                 resulting_opaque_rect);
@@ -108,11 +107,12 @@ void BitmapContentLayerUpdater::ReduceMemoryUsage() {
 }
 
 void BitmapContentLayerUpdater::SetOpaque(bool opaque) {
-  if (opaque != opaque_) {
+  if (opaque != layer_is_opaque_) {
     canvas_.clear();
     canvas_size_ = gfx::Size();
   }
-  opaque_ = opaque;
+
+  ContentLayerUpdater::SetOpaque(opaque);
 }
 
 }  // namespace cc