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

base/metrics/user_metrics_action.h

Index: base/metrics/user_metrics_action.h
diff --git a/base/metrics/user_metrics_action.h b/base/metrics/user_metrics_action.h
index 8c195b3e80341758f9dec4d4915db59b7823e423..3eca3ddb8b18d2ced454ddf0f564b59272c6b0ad 100644
--- a/base/metrics/user_metrics_action.h
+++ b/base/metrics/user_metrics_action.h
@@ -10,13 +10,12 @@ 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_;