Adding DRP specfic UMA for FirstContentfulPaint

chrome/chrome_tests_unit.gypi

Index: chrome/chrome_tests_unit.gypi
diff --git a/chrome/chrome_tests_unit.gypi b/chrome/chrome_tests_unit.gypi
index c0bbb80166e10db66ab04c7dabd9e05e6e81eb22..07a1157d90d4a328f42db7efd1afd59522f8280e 100644
--- a/chrome/chrome_tests_unit.gypi
+++ b/chrome/chrome_tests_unit.gypi
@@ -146,20 +146,21 @@
       'browser/net/net_error_tab_helper_unittest.cc',
       'browser/net/predictor_unittest.cc',
       'browser/net/probe_message_unittest.cc',
       'browser/net/quota_policy_channel_id_store_unittest.cc',
       'browser/net/safe_search_util_unittest.cc',
       'browser/net/spdyproxy/data_reduction_proxy_chrome_settings_unittest.cc',
       'browser/net/spdyproxy/data_reduction_proxy_settings_unittest_android.cc',
       'browser/net/url_info_unittest.cc',
       'browser/page_load_metrics/observers/aborts_page_load_metrics_observer_unittest.cc',
       'browser/page_load_metrics/observers/core_page_load_metrics_observer_unittest.cc',
+      'browser/page_load_metrics/observers/data_reduction_proxy_metrics_observer_unittest.cc',
       'browser/page_load_metrics/observers/from_gws_page_load_metrics_observer_unittest.cc',
       'browser/page_load_metrics/observers/google_captcha_observer_unittest.cc',
       'browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.cc',
       'browser/page_load_metrics/observers/page_load_metrics_observer_test_harness.h',
       'browser/password_manager/chrome_password_manager_client_unittest.cc',
       'browser/password_manager/password_manager_internals_service_unittest.cc',
       'browser/password_manager/password_store_mac_unittest.cc',
       'browser/password_manager/password_store_proxy_mac_unittest.cc',
       'browser/password_manager/password_store_win_unittest.cc',
       'browser/password_manager/password_store_x_unittest.cc',