Implement cc::Selection<gfx::SelectionBound> StructTraits

cc/ipc/traits_test_service.mojom

Index: cc/ipc/traits_test_service.mojom
diff --git a/cc/ipc/traits_test_service.mojom b/cc/ipc/traits_test_service.mojom
index a88b09a769792786634cb5a3c42b3b72bdaa8456..0d807c25ef42552cbbaafbb5b606afb77155fe99 100644
--- a/cc/ipc/traits_test_service.mojom
+++ b/cc/ipc/traits_test_service.mojom
@@ -7,6 +7,7 @@ module cc.mojom;
 import "cc/ipc/begin_frame_args.mojom";
 import "cc/ipc/render_pass_id.mojom";
 import "cc/ipc/returned_resource.mojom";
+import "cc/ipc/selection.mojom";
 import "cc/ipc/shared_quad_state.mojom";
 import "cc/ipc/surface_id.mojom";
 import "cc/ipc/transferable_resource.mojom";
@@ -25,6 +26,9 @@ interface TraitsTestService {
   EchoReturnedResource(ReturnedResource r) => (ReturnedResource pass);
 
   [Sync]
+  EchoSelection(Selection s) => (Selection pass);
+
+  [Sync]
   EchoSharedQuadState(SharedQuadState s) => (SharedQuadState pass);
 
   [Sync]