[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;
 
     // 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_;
   };