Fix DevToolsBeforeUnloadTest.TestDevToolsOnDevTools flakiness

BUG=333554,323847

Review URL: https://codereview.chromium.org/142933006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246026 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246026
Fix problem with MediaStreamTrack::Stop while generating a MediaStream.

The bug is that a request is deleted if it has no opened devices regardless if this request has anything to do with the device we are trying to stop.
The fix is to make sure a request is only deleted if the request actually used the device that we are closing. 

BUG=332386

Review URL: https://codereview.chromium.org/143373002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246027 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246027