cc: Fix MSAA when threaded GPU rasterization is enabled.

cc/resources/gpu_rasterizer.cc

Index: cc/resources/gpu_rasterizer.cc
diff --git a/cc/resources/gpu_rasterizer.cc b/cc/resources/gpu_rasterizer.cc
index e0097f87ddba5998e01231549edb97cdca885681..6e318edabbe80a2c670eef3baf96abf9dd36d990 100644
--- a/cc/resources/gpu_rasterizer.cc
+++ b/cc/resources/gpu_rasterizer.cc
@@ -123,7 +123,7 @@ void GpuRasterizer::RasterizeSource(
     SkMultiPictureDraw multi_picture_draw;
     multi_picture_draw.add(write_lock->sk_surface()->getCanvas(),
                            picture.get());
-    multi_picture_draw.draw(false);
+    multi_picture_draw.draw(msaa_sample_count_ > 0);
     write_lock->ReleaseSkSurface();
   }
 }