Revert "Revert 236071 "Allow TracingController output trace data to spec...""

Fixed unused result warning of fwrite call.

> Allow TracingController output trace data to specified file
>
> Sometimes we need to let TracingController output traces to specified
> file, e.g. trace-startup (which will be migrated from TraceController
> to TracingController).
>
> Also fixed the problem of IO operations in UI thread.
>
> BUG=none
> TEST=TracingControllerTest.EnableAndDisableRecordingWithFilePath
> TEST=TracingControllerTest.EnableCaptureAndDisableMonitoringWithFilePath
> R=joi@chromium.org, nduca@chromium.org
>
> Review URL: https://codereview.chromium.org/66893003

This reverts commit 5f0d8c08989b900b61f7be1ee97d3c237dba4a76.

TBR=yzshen
BUG=none

Review URL: https://codereview.chromium.org/77273003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236100 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236100