Add UpdateCurrentAppInfo() interface to record info about current app, including

chromecast/base/metrics/cast_metrics_helper.h

Index: chromecast/base/metrics/cast_metrics_helper.h
diff --git a/chromecast/base/metrics/cast_metrics_helper.h b/chromecast/base/metrics/cast_metrics_helper.h
index 5e76b796580f2195d136e828cfcfdc7e18eeee48..9583c181c392b6d389da6ff0bf68152be2dd6d29 100644
--- a/chromecast/base/metrics/cast_metrics_helper.h
+++ b/chromecast/base/metrics/cast_metrics_helper.h
@@ -53,6 +53,10 @@ class CastMetricsHelper {
 
   // This function stores the name and startup time of the active application.
   virtual void TagAppStart(const std::string& app_name);
+  // This function update the info of current active application.

[gunsch, 2014/12/10 16:54:18]

Remove "This function"

"update" --> "Updates"

"of" --> "for"

[gfhuang, 2014/12/10 22:02:41]

Done.

+  virtual void UpdateCurrentAppInfo(const std::string& app_id,
+                                    const std::string& session_id,
+                                    const std::string& sdk_version);
 
   // Logs UMA record for media play/pause user actions.
   virtual void LogMediaPlay();
@@ -78,9 +82,14 @@ class CastMetricsHelper {
                                     int delayed_frames, int error_frames);
 
   // Returns metrics name with app name between prefix and suffix.
+  // This is used by histograms.
   virtual std::string GetMetricsNameWithAppName(
       const std::string& prefix,
       const std::string& suffix) const;
+  // Returns metrics name with app_id/session_id/sdk_version.
+  // This is used by actions, so far MediaPlay/MediaPause only.

[gunsch, 2014/12/10 16:54:19]

This comment is bound to become obsolete. Can you remove the reference to
MediaPlay/MediaPause?

Also, are "used by actions" and "used by histograms" restrictions? If so, can
you encode them into the method names? If not, then you should remove the
comments.

[gfhuang, 2014/12/10 22:02:41]

Done.

+  virtual std::string GetMetricsNameWithAppInfo(

[gunsch, 2014/12/10 22:43:58]

does anyone call this externally? seems to me like it should be a private method

+      const std::string& action_name) const;
 
   // Provides a MetricsSink instance to delegate UMA event logging.
   // Once the delegate interface is set, CastMetricsHelper will not log UMA
@@ -118,6 +127,9 @@ class CastMetricsHelper {
 
   // Currently running app name. Used to construct histogram name.
   std::string app_name_;
+  std::string app_id_;
+  std::string session_id_;
+  std::string sdk_version_;
 
   // Whether a new app start time has been stored but not recorded.
   // After the startup time has been used to generate an UMA event,