color: Clarify default behaviors

cc/ipc/struct_traits_unittest.cc

Index: cc/ipc/struct_traits_unittest.cc
diff --git a/cc/ipc/struct_traits_unittest.cc b/cc/ipc/struct_traits_unittest.cc
index 1b90b4a5498bb3a2b6964b5716a3e2ea6d7c7231..dbcb4aaac6377d3bd08255f26c98be9cecbd93e1 100644
--- a/cc/ipc/struct_traits_unittest.cc
+++ b/cc/ipc/struct_traits_unittest.cc
@@ -968,7 +968,7 @@ TEST_F(StructTraitsTest, TextureMailbox) {
   const bool is_overlay_candidate = true;
   const bool secure_output_only = true;
   const bool nearest_neighbor = true;
-  const gfx::ColorSpace color_space(4, 5, 9, gfx::ColorSpace::RangeID::LIMITED);
+  const gfx::ColorSpace color_space = gfx::ColorSpace::CreateREC709();
 #if defined(OS_ANDROID)
   const bool is_backed_by_surface_texture = true;
   const bool wants_promotion_hint = true;