Use a WeakPtr in SpeechRecognizerImpl::AbortRecognition

It seems that during shutdown, the object can go away before the posted
task runs.

Thanks to Miyoung Shin for looking into this.

Bug: 1018677
Change-Id: I1b3c7947eb3110ae6538249106a87f5c56f6238c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1989069Reviewed-by: Primiano Tucci <primiano@chromium.org>
Reviewed-by: Tommi <tommi@chromium.org>
Reviewed-by: Olga Sharonova <olka@chromium.org>
Commit-Queue: Olga Sharonova <olka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#729694}

content/browser/speech/speech_recognizer_impl.cc

@@ -230,7 +230,8 @@ void SpeechRecognizerImpl::StartRecognition(const std::string& device_id) {
 
 void SpeechRecognizerImpl::AbortRecognition() {
   base::PostTask(FROM_HERE, {BrowserThread::IO},
-                 base::BindOnce(&SpeechRecognizerImpl::DispatchEvent, this,
+                 base::BindOnce(&SpeechRecognizerImpl::DispatchEvent,
+                                weak_ptr_factory_.GetWeakPtr(),
                                 FSMEventArgs(EVENT_ABORT)));
 }