tracing: get rid of files in TracingController interface

components/feedback/tracing_manager.h

 // Copyright 2014 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 COMPONENTS_FEEDBACK_TRACING_MANAGER_H_
 #define COMPONENTS_FEEDBACK_TRACING_MANAGER_H_
 
 #include <map>
 #include <string>
 
@@ skipping 40 matching lines @@
   // returned via |callback|.  Returns false on failure.
   bool GetTraceData(int id, const TraceDataCallback& callback);
 
   // Discard the data for trace |id|.
   void DiscardTraceData(int id);
 
  private:
   TracingManager();
 
   void StartTracing();
-  void OnTraceDataCollected(const base::FilePath& path);
+  void OnTraceDataCollected(const std::string& trace_data);
 
   // ID of the trace that is being collected.
   int current_trace_id_;
 
   // Mapping of trace ID to trace data.
   std::map<int, scoped_refptr<base::RefCountedString> > trace_data_;
 
   // Callback for the current trace request.
   TraceDataCallback trace_callback_;
 
   base::WeakPtrFactory<TracingManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TracingManager);
 };
 
 #endif  // COMPONENTS_FEEDBACK_TRACING_MANAGER_H_