Added UMA metrics for display settings UI in the status area.

base/metrics/user_metrics_action.h

 // 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.
 
 #ifndef BASE_METRICS_USER_METRICS_ACTION_H_
 #define BASE_METRICS_USER_METRICS_ACTION_H_
 
 namespace base {
 
 // UserMetricsAction exists purely to standardize on the parameters passed to
 // UserMetrics. That way, our toolset can scan the source code reliable for
 // constructors and extract the associated string constants.
-// WARNING: When using UserMetricsAction, UserMetricsAction and a string literal
-// parameter must be on the same line, e.g.
-//   RecordAction(UserMetricsAction("my extremely long action name"));
-// or
-//   RenderThread::Get()->RecordAction(
-//       UserMetricsAction("my extremely long action name"));
-// because otherwise our processing scripts won't pick up on new actions.
+// WARNING: When using UserMetricsAction you should use a string literal
+// parameter e.g.
+//   RecordAction(UserMetricsAction("my action name"));
+// This ensures that our processing scripts can associate this action's hash
+// with its metric name. Therefore, it will be possible to retrieve the metric
+// name from the hash later on.
 // Please see tools/metrics/actions/extract_actions.py for details.
 struct UserMetricsAction {
   const char* str_;
   explicit UserMetricsAction(const char* str) : str_(str) {}
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_USER_METRICS_ACTION_H_