Skip clearing the canvas before painting the contents of opaque layers

cc/resources/skpicture_content_layer_updater.cc

Index: cc/resources/skpicture_content_layer_updater.cc
diff --git a/cc/resources/skpicture_content_layer_updater.cc b/cc/resources/skpicture_content_layer_updater.cc
index e44dbc252051b965d52c55acce8b691dff9f38a2..f1cf45439a70bcb5ed22ff496e116349243ae242 100644
--- a/cc/resources/skpicture_content_layer_updater.cc
+++ b/cc/resources/skpicture_content_layer_updater.cc
@@ -17,8 +17,7 @@ SkPictureContentLayerUpdater::SkPictureContentLayerUpdater(
     scoped_ptr<LayerPainter> painter,
     RenderingStatsInstrumentation* stats_instrumentation,
     int layer_id)
-    : ContentLayerUpdater(painter.Pass(), stats_instrumentation, layer_id),
-      layer_is_opaque_(false) {}
+    : ContentLayerUpdater(painter.Pass(), stats_instrumentation, layer_id) {}
 
 SkPictureContentLayerUpdater::~SkPictureContentLayerUpdater() {}
 
@@ -49,8 +48,4 @@ void SkPictureContentLayerUpdater::DrawPicture(SkCanvas* canvas) {
   canvas->drawPicture(picture_);
 }
 
-void SkPictureContentLayerUpdater::SetOpaque(bool opaque) {
-  layer_is_opaque_ = opaque;
-}
-
 }  // namespace cc