Add chrome test support target to GN build.

chrome/common/BUILD.gn

 # Copyright 2014 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.
 
 import("//tools/grit/grit_rule.gni")
 
 gypi_values = exec_script(
     "//build/gypi_to_gn.py",
     [ rebase_path("../chrome_common.gypi") ],
     "scope",
@@ skipping 273 matching lines @@
     "//components/bookmarks/common",
     "//third_party/widevine/cdm:version_h",
   ]
 
   if (enable_nacl) {
     deps += [
       #'../components/nacl.gyp:nacl_switches',  TODO(GYP)
     ]
   }
 }
+
+source_set("test_support") {
+  testonly = true
+  visibility = [ "//chrome/test:test_support" ]
+
+  sources = [
+    "extensions/extension_test_util.cc",
+    "extensions/extension_test_util.h",
+  ]
+
+  deps = [
+    ":common",
+    "//base",
+    "//testing/gtest",
+  ]
+
+  if (is_win || is_mac) {
+    sources += [
+      "media_galleries/picasa_test_util.cc",
+      "media_galleries/picasa_test_util.cc",
+      "media_galleries/pmp_test_util.cc",
+      "media_galleries/pmp_test_util.h",
+    ]
+  }
+
+}