Bug 1121669 - Add a mutex around mFlushTimer to deal with write appearing to other threads in an inconsistent order. r=jseward.

MozReview-Commit-ID: 56r9PsEf8Jv

parser/html/nsHtml5StreamParser.h

@@ -544,6 +544,12 @@ class nsHtml5StreamParser : public nsICharsetDetectionObserver {
      */
     nsCOMPtr<nsITimer>            mFlushTimer;
 
+    /**
+     * Mutex for protecting access to mFlushTimer (but not for the two
+     * mFlushTimerFoo booleans below).
+     */
+    mozilla::Mutex                mFlushTimerMutex;
+
     /**
      * Keeps track whether mFlushTimer has been armed. Unfortunately,
      * nsITimer doesn't enable querying this from the timer itself.