cc: Clean up LayerTreeTest and TestHooks.

cc/BUILD.gn

Index: cc/BUILD.gn
diff --git a/cc/BUILD.gn b/cc/BUILD.gn
index 8bdc2c733ac05b38d06eea063f8aa7de7396321c..b69480ad823f3596d9820f8d4857489b97c4cb14 100644
--- a/cc/BUILD.gn
+++ b/cc/BUILD.gn
@@ -699,12 +699,6 @@ static_library("test_support") {
     "test/pixel_test_software_output_device.h",
     "test/pixel_test_utils.cc",
     "test/pixel_test_utils.h",
-    "test/proxy_impl_for_test.cc",
-    "test/proxy_impl_for_test.h",
-    "test/proxy_main_for_test.cc",
-    "test/proxy_main_for_test.h",
-    "test/remote_channel_impl_for_test.cc",
-    "test/remote_channel_impl_for_test.h",
     "test/remote_proto_channel_bridge.cc",
     "test/remote_proto_channel_bridge.h",
     "test/render_pass_test_utils.cc",
@@ -941,9 +935,6 @@ test("cc_unittests") {
     "trees/occlusion_unittest.cc",
     "trees/property_tree_unittest.cc",
     "trees/proxy_common_unittest.cc",
-    "trees/proxy_impl_unittest.cc",
-    "trees/remote_channel_unittest.cc",
-    "trees/threaded_channel_unittest.cc",
     "trees/tree_synchronizer_unittest.cc",
 
     # Surfaces test files.