Add optional public header checking to GN build

tools/gn/secondary/testing/gmock/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 config("gmock_config") {
   # Gmock headers need to be able to find themselves.
   include_dirs = [ "include" ]
 }
 
 static_library("gmock") {
@@ skipping 10 matching lines @@
     "include/gmock/gmock.h",
     "include/gmock/internal/gmock-generated-internal-utils.h",
     "include/gmock/internal/gmock-internal-utils.h",
     "include/gmock/internal/gmock-port.h",
     #"src/gmock-all.cc",  # Not needed by our build.
     "src/gmock-cardinalities.cc",
     "src/gmock-internal-utils.cc",
     "src/gmock-matchers.cc",
     "src/gmock-spec-builders.cc",
     "src/gmock.cc",
-    "gmock_mutant.h",  # gMock helpers
+    "../gmock_mutant.h",  # gMock helpers
   ]
 
   # This project includes some stuff form gtest's guts.
   include_dirs = [ "../gtest/include" ]
 
   direct_dependent_configs = [
     ":gmock_config",
     "//testing/gtest:gtest_config",
   ]
+
+  deps = [ "//base" ]
 }
 
 static_library("gmock_main") {
   sources = [ "src/gmock_main.cc" ]
   deps = [ ":gmock" ]
 }