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The introduction of the MediaRequestPermission (i.e. infobar) has
opened a race window which causes a recognition session to be aborted
twice, causing a consequent crash on the renderer.
The race window is the following:
1) Session 1 is started (SpeechRecognitionManagerImpl::StartSession)
2) Security checks for session 1 are started asynchronously
   (delegate_->CheckRecognitionIsAllowed).
3) Session 2 is started. This causes an immediate abort of session 1.
4) The oustanding security check for session 1 completes and returns
   a nack. The nack causes an abort of session 1 (in
   RecognitionAllowedCallback). However, session 1 was already aborted
   in 3).
5) The double abort is not tolerated by the renderer, which crashes.

This CL closes the race window with a not-so-elegant fix.
A refactoring of the speech_recognition_manager_impl.cc is STRONGLY
adviced (Hint: use and extend the already existing FSM to keep track
of the asynchronous completion of security checks. Don't introduce
extra state with extra variables).

BUG=296690,116954

Review URL: https://codereview.chromium.org/25550003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226523 0039d316-1c4b-4281-b951-d872f2087c98