[2/5] Disable transformed rasterization if layer is opaque

cc/layers/picture_layer_impl.cc

Index: cc/layers/picture_layer_impl.cc
diff --git a/cc/layers/picture_layer_impl.cc b/cc/layers/picture_layer_impl.cc
index ccffabe01bde91876e55748e1d1e6bc45aaf3d4a..03ff4553cfd82e4f9cea5791b38851d9e7386687 100644
--- a/cc/layers/picture_layer_impl.cc
+++ b/cc/layers/picture_layer_impl.cc
@@ -662,6 +662,12 @@ void PictureLayerImpl::NotifyTileStateChanged(const Tile* tile) {
   }
 }
 
+SimpleEnclosedRegion PictureLayerImpl::VisibleOpaqueRegion() const {
+  if (use_transformed_rasterization_)
+    return SimpleEnclosedRegion();

[enne (OOO), 2017/01/03 22:53:08]

Why not VisibleOpaqueRegion but Inset by 1?

[trchen, 2017/01/14 00:46:46]

Because it depends on the actual raster scale. For example, a layer of size (99,
99) with raster scale 0.25, its opaque region in raster space would be
EnclosedRect(ScaleRect(Rect(99,99), 0.25)) == Rect(24, 24). When mapped back to
the layer space, it's only (96, 96).

For non-transformed-rasterized layer it is fine because the edge pixel will be
filled with opaque background color.

+  return LayerImpl::VisibleOpaqueRegion();
+}
+
 void PictureLayerImpl::DidBeginTracing() {
   raster_source_->DidBeginTracing();
 }