Move the thread hop for UMA user actions from content:: to base::.

base/test/user_action_tester.h

Index: base/test/user_action_tester.h
diff --git a/base/test/user_action_tester.h b/base/test/user_action_tester.h
index 620988b2b8dceac02fd5f7abe63cc0a3e3c1b0e3..88bc632c47f6d939f032ffe8a11e540c4934dd6e 100644
--- a/base/test/user_action_tester.h
+++ b/base/test/user_action_tester.h
@@ -36,6 +36,9 @@ class UserActionTester {
   // A map that tracks the number of times a user action has occurred.
   UserActionCountMap count_map_;
 
+  // A test task runner used by user metrics.
+  scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
+
   // The callback that is added to the global action callback list.
   base::ActionCallback action_callback_;