Scale the ALPHA_THRESHOLD filter's region based on the device scale factor.

cc/trees/layer_tree_host_unittest_delegated.cc

Index: cc/trees/layer_tree_host_unittest_delegated.cc
diff --git a/cc/trees/layer_tree_host_unittest_delegated.cc b/cc/trees/layer_tree_host_unittest_delegated.cc
index a181b09e0d4ae5ad3582507bf8b6505852f7f994..c13465473f61e77b2667bf6470f6c325ea921e84 100644
--- a/cc/trees/layer_tree_host_unittest_delegated.cc
+++ b/cc/trees/layer_tree_host_unittest_delegated.cc
@@ -194,7 +194,8 @@ class LayerTreeHostDelegatedTest : public LayerTreeTest {
                  damage_rect,
                  gfx::Rect(0, 0, 1, 1),  // mask_uv_rect
                  filters,
-                 background_filters);
+                 background_filters,
+                 gfx::Vector2dF(1.f, 1.f));
     frame->render_pass_list[0]->quad_list.push_back(quad.PassAs<DrawQuad>());
   }