Added test support to observe and verify UMA user actions during tests.

base/base.gyp

Index: base/base.gyp
diff --git a/base/base.gyp b/base/base.gyp
index 23f6d565b876c76ba0973a5945e3ccf084ac3fc2..0a455fb0ea1dd7c4d8b82401c5c63d166b204dc3 100644
--- a/base/base.gyp
+++ b/base/base.gyp
@@ -631,6 +631,7 @@
         'test/test_pending_task_unittest.cc',
         'test/test_reg_util_win_unittest.cc',
         'test/trace_event_analyzer_unittest.cc',
+        'test/user_action_tester_unittest.cc',
         'threading/non_thread_safe_unittest.cc',
         'threading/platform_thread_unittest.cc',
         'threading/sequenced_worker_pool_unittest.cc',
@@ -1009,6 +1010,8 @@
         'test/trace_event_analyzer.h',
         'test/trace_to_file.cc',
         'test/trace_to_file.h',
+        'test/user_action_tester.cc',
+        'test/user_action_tester.h',
         'test/values_test_util.cc',
         'test/values_test_util.h',
       ],