[Tracing Clock Sync] Add TracingAgent interface in Chrome

content/public/browser/tracing_controller.h

Index: content/public/browser/tracing_controller.h
diff --git a/content/public/browser/tracing_controller.h b/content/public/browser/tracing_controller.h
index 6467e95212fbb3a2c976274cf920154c81918773..95a8be3608264853bd46156c3dc4a44aebf672f5 100644
--- a/content/public/browser/tracing_controller.h
+++ b/content/public/browser/tracing_controller.h
@@ -37,25 +37,29 @@ class TracingController {
   class CONTENT_EXPORT TraceDataSink
       : public base::RefCountedThreadSafe<TraceDataSink> {
    public:
+    TraceDataSink();
+
     virtual void AddTraceChunk(const std::string& chunk) {}
-    virtual void SetSystemTrace(const std::string& data) {}
+
+    virtual void AddAgentTrace(const std::string& trace_label,
+                               const std::string& trace_data);
+    virtual const std::map<std::string, std::string>&
+        GetAdditionalTracingAgentTrace() const;

[no sievers, 2015/12/10 19:35:20]

can you document what the two strings in the returned map are.
And also document somewhere what an agent is and what this method does? Maybe
then the interesting method name will make some sense (i.e. why 'additional',
why 'tracing agent' and why 'trace') :)

[Zhen Wang, 2015/12/10 21:09:27]

Done. This function should corresponds to AddAgentTrace(). Since it is only
called by its child classes, I make it protected now.

 
     // Notice that TracingController adds some default metadata when
     // DisableRecording is called, which may override metadata that you would
     // set beforehand in case of key collision.
     virtual void AddMetadata(const base::DictionaryValue& data);
     virtual const base::DictionaryValue& GetMetadata() const;
-    // TODO(prabhur) Replace all the Set* functions with a generic function:
-    // TraceDataSink::AppendAdditionalData(const std::string& name,
-    // const std::string& trace_data)
-    virtual void SetPowerTrace(const std::string& data) {}
+
     virtual void Close() {}
 
    protected:
     friend class base::RefCountedThreadSafe<TraceDataSink>;
-    virtual ~TraceDataSink() {}
+    virtual ~TraceDataSink();
 
    private:
+    std::map<std::string, std::string> additional_tracing_agent_trace_;
     base::DictionaryValue metadata_;
   };