cc: Move surfaces hittesting test helpers out to a separate file

cc/BUILD.gn

Index: cc/BUILD.gn
diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index c24430b382b902c793f24f6de163541e59691cd7..799e1cc1b0f52ee6c856f27cafe4aecead2c8396 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn
@@ -637,6 +637,10 @@ source_set("test_support") {
     "test/skia_common.h",
     "test/solid_color_content_layer_client.cc",
     "test/solid_color_content_layer_client.h",
+    "test/surface_aggregator_test_helpers.cc",
+    "test/surface_aggregator_test_helpers.h",
+    "test/surface_hittest_test_helpers.cc",
+    "test/surface_hittest_test_helpers.h",
     "test/test_context_provider.cc",
     "test/test_context_provider.h",
     "test/test_context_support.cc",
@@ -839,8 +843,6 @@ test("cc_unittests") {
     # Surfaces test files.
     "surfaces/display_scheduler_unittest.cc",
     "surfaces/display_unittest.cc",
-    "surfaces/surface_aggregator_test_helpers.cc",
-    "surfaces/surface_aggregator_test_helpers.h",
     "surfaces/surface_aggregator_unittest.cc",
     "surfaces/surface_display_output_surface_unittest.cc",
     "surfaces/surface_factory_unittest.cc",