Pass MetricsServiceClient into MetricsService, and create a simple stubbed TestMetricsServiceClient…

chrome/chrome_tests_unit.gypi

 # Copyright 2012 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.
 {
   'targets': [
     {
       # This target contains mocks and test utilities that don't belong in
       # production libraries but are used by more than one test executable.
       'target_name': 'test_support_common',
       'type': 'static_library',
       'dependencies': [
         # NOTE: New dependencies should generally be added in the OS!="ios"
         # dependencies block below, rather than here.
         'browser',
         'chrome_resources.gyp:chrome_resources',
         'chrome_resources.gyp:chrome_strings',
         'chrome_resources.gyp:theme_resources',
         'common',
         '../base/base.gyp:base_prefs_test_support',
         '../base/base.gyp:test_support_base',
+        '../components/components.gyp:bookmarks_test_support',
+        '../components/components.gyp:metrics_test_support',
         '../components/components.gyp:password_manager_core_browser_test_support',
         '../components/components.gyp:signin_core_browser_test_support',
         '../components/components.gyp:sync_driver_test_support',
-        '../components/components.gyp:bookmarks_test_support',
         '../content/content.gyp:content_app_both',
         '../content/content_shell_and_tests.gyp:test_support_content',
         '../net/net.gyp:net',
         '../net/net.gyp:net_test_support',
         '../skia/skia.gyp:skia',
         '../sql/sql.gyp:sql',
         '../sql/sql.gyp:test_support_sql',
         '../sync/sync.gyp:sync',
         '../testing/gmock.gyp:gmock',
         '../testing/gtest.gyp:gtest',
@@ skipping 2801 matching lines @@
               # more details.
               'DebugInformationFormat': '3',
               'ProgramDataBaseFileName': '<(PRODUCT_DIR)/unit_tests.exe.pdb',
             },
           },
         },
       ],
     }],
   ],  # 'conditions'
 }