Add a command-line flag to set GPU rasterization multisampling.

cc/test/layer_tree_pixel_resource_test.cc

Index: cc/test/layer_tree_pixel_resource_test.cc
diff --git a/cc/test/layer_tree_pixel_resource_test.cc b/cc/test/layer_tree_pixel_resource_test.cc
index e3df017489fa10d60968342c5f474d149859cb5e..7eb47c50006ac99762805ce96c3611e540e3f662 100644
--- a/cc/test/layer_tree_pixel_resource_test.cc
+++ b/cc/test/layer_tree_pixel_resource_test.cc
@@ -140,7 +140,7 @@ scoped_ptr<Rasterizer> LayerTreeHostPixelResourceTest::CreateRasterizer(
     case GPU_TILE_TASK_WORKER_POOL:
       EXPECT_TRUE(context_provider);
       return GpuRasterizer::Create(context_provider, resource_provider,
-                                   use_distance_field_text, false);
+                                   use_distance_field_text, false, 0);
   }
   NOTREACHED();
   return nullptr;