Have mock speech recognizer reset and release its recognizer upon ending.

Take care of leaks attributed to this mock object - it unnecessarily
retaining a WebSpeechRecognitionHandle beyond completion of the final
'ended' notification to it.

R=dmazzoni
BUG=506529

Review URL: https://codereview.chromium.org/1737953003

Cr-Commit-Position: refs/heads/master@{#378252}
1 file changed