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..26fda8dde37fa319bff6fbff28fe044da58ef84a 100644
--- a/cc/layers/scrollbar_layer_impl.cc
+++ b/cc/layers/scrollbar_layer_impl.cc
@@ -118,6 +118,7 @@ void ScrollbarLayerImpl::AppendQuads(QuadSink* quad_sink,
                  premultipled_alpha,
                  uv_top_left,
                  uv_bottom_right,
+                 SK_ColorTRANSPARENT,
                  opacity,
                  flipped);
     quad_sink->Append(quad.PassAs<DrawQuad>(), append_quads_data);
@@ -141,6 +142,7 @@ void ScrollbarLayerImpl::AppendQuads(QuadSink* quad_sink,
                  premultipled_alpha,
                  uv_top_left,
                  uv_bottom_right,
+                 SK_ColorTRANSPARENT,
                  opacity,
                  flipped);
     quad_sink->Append(quad.PassAs<DrawQuad>(), append_quads_data);