Allow TracingController to output trace data to specified file

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 "base/debug/trace_event.h"
 #include "content/common/content_export.h"
 
@@ skipping 57 matching lines @@
   //
   // Child processes typically are caching trace data and only rarely flush
   // and send trace data back to the browser process. That is because it may be
   // an expensive operation to send the trace data over IPC, and we would like
   // to avoid much runtime overhead of tracing. So, to end tracing, we must
   // asynchronously ask all child processes to flush any pending trace data.
   //
   // Once all child processes have acked to the DisableRecording request,
   // TracingFileResultCallback will be called back with a file that contains
   // the traced data.
-  typedef base::Callback<void(scoped_ptr<base::FilePath>)>
-      TracingFileResultCallback;
-  virtual bool DisableRecording(const TracingFileResultCallback& callback) = 0;
+  //
+  // Trace data will be written into |result_file_path| if it is not empty, or
+  // into a temporary file. The actual file path will be passed to |callback|.
+  //
+  // If |result_file_path| is empty and |callback| is null, trace data won't be

[dsinclair, 2013/11/18 16:32:18]

Isn't this an OR instead of an AND.

[Xianzhu, 2013/11/18 21:50:39]

Used 'AND' because I thought the following might be a useful case: the caller
wants to save the traces into a file but don't care when the async process
finishes. The current impl is following the comment here.

[Xianzhu, 2013/11/18 21:56:09]

Note this is also consistent with other methods that will do the actual thing
(if it's meaningful) when the callback is null.

+  // written to any file.
+  typedef base::Callback<void(const base::FilePath&)> TracingFileResultCallback;
+  virtual bool DisableRecording(const base::FilePath& result_file_path,
+                                const TracingFileResultCallback& callback) = 0;
 
   // Start monitoring on all processes.
   //
   // Monitoring begins immediately locally, and asynchronously on child
   // processes as soon as they receive the EnableMonitoring request.
   //
   // Once all child processes have acked to the EnableMonitoring request,
   // EnableMonitoringDoneCallback will be called back.
   //
   // |filter| is a filter to control what category groups should be traced.
@@ skipping 21 matching lines @@
   //
   // Child processes typically are caching trace data and only rarely flush
   // and send trace data back to the browser process. That is because it may be
   // an expensive operation to send the trace data over IPC, and we would like
   // to avoid much runtime overhead of tracing. So, to end tracing, we must
   // asynchronously ask all child processes to flush any pending trace data.
   //
   // Once all child processes have acked to the CaptureMonitoringSnapshot
   // request, TracingFileResultCallback will be called back with a file that
   // contains the traced data.
+  //
+  // Trace data will be written into |result_file_path| if it is not empty, or
+  // into a temporary file. The actual file path will be passed to |callback|.
+  //
+  // If |result_file_path| is empty and |callback| is null, trace data won't be
+  // written to any file.
   virtual void CaptureMonitoringSnapshot(
+      const base::FilePath& result_file_path,
       const TracingFileResultCallback& callback) = 0;
 
  protected:
   virtual ~TracingController() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_TRACING_CONTROLLER_H_