[Tracing Clock Sync] Add TracingAgent interface in Chrome

content/public/browser/tracing_controller.h

 // Copyright 2013 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 CONTENT_PUBLIC_BROWSER_TRACING_CONTROLLER_H_
 #define CONTENT_PUBLIC_BROWSER_TRACING_CONTROLLER_H_
 
 #include <set>
 #include <string>
 
@@ skipping 19 matching lines @@
   // An interface for trace data consumer. An implemnentation of this interface
   // is passed to either DisableTracing() or CaptureMonitoringSnapshot() and
   // receives the trace data followed by a notification that all child processes
   // have completed tracing and the data collection is over.
   // All methods are called on the UI thread.
   // Close method will be called exactly once and no methods will be
   // called after that.
   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_;
   };
 
   // An implementation of this interface is passed when constructing a
   // TraceDataSink, and receives chunks of the final trace data as it's being
   // constructed.
   // Methods may be called from any thread.
   class CONTENT_EXPORT TraceDataEndpoint
       : public base::RefCountedThreadSafe<TraceDataEndpoint> {
    public:
@@ skipping 156 matching lines @@
   // Check if the tracing system is tracing
   virtual bool IsTracing() const = 0;
 
  protected:
   virtual ~TracingController() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_TRACING_CONTROLLER_H_