GitLab

ChromeSRMDelegate should not be reading the WebContents* back from
  WebContentsObserver after it has explicitly set to observe nullptr
  WebContents.
This was introduced by my earlier CL: r330213, I never tested the
  feature from NTP.

BUG=489182, 489157
Test=1) From new tab page, click on the mic beside search box,
  feed it some search query, it should not crash chrome.
2) Similar to step #1, but before the query completes, close the
  tab, observe no crash.

Review URL: https://codereview.chromium.org/1134773004

Cr-Commit-Position: refs/heads/master@{#330784}