Blend TextureLayer background-color at draw time.

cc/layers/scrollbar_layer_impl.cc

Index: cc/layers/scrollbar_layer_impl.cc
diff --git a/cc/layers/scrollbar_layer_impl.cc b/cc/layers/scrollbar_layer_impl.cc
index 4160bf0f5b4ff800e480e0312fbc3227174da93b..157635f0899e5c9316336cccb3e1d65564608ac7 100644
--- a/cc/layers/scrollbar_layer_impl.cc
+++ b/cc/layers/scrollbar_layer_impl.cc
@@ -119,6 +119,7 @@ void ScrollbarLayerImpl::AppendQuads(QuadSink* quad_sink,
                  uv_top_left,
                  uv_bottom_right,
                  opacity,
+                 SK_ColorTRANSPARENT,
                  flipped);
     quad_sink->Append(quad.PassAs<DrawQuad>(), append_quads_data);
   }
@@ -142,6 +143,7 @@ void ScrollbarLayerImpl::AppendQuads(QuadSink* quad_sink,
                  uv_top_left,
                  uv_bottom_right,
                  opacity,
+                 SK_ColorTRANSPARENT,
                  flipped);
     quad_sink->Append(quad.PassAs<DrawQuad>(), append_quads_data);
   }