DevTools: Fix timeline stop recording race.

The recording could have already being stopped by the time auto stop kicks in.

BUG=832332

Change-Id: Ia25f8b7c3fc9c0ba62956ed5d8286fdcc786cdee
Reviewed-on: https://chromium-review.googlesource.com/1011399Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550655}

third_party/blink/renderer/devtools/front_end/timeline/TimelinePanel.js

@@ -760,9 +760,8 @@ Timeline.TimelinePanel = class extends UI.Panel {
     await new Promise(r => setTimeout(r, this._millisecondsToRecordAfterLoadEvent));
 
     // Check if we're still in the same recording session.
-    if (controller !== this._controller)
+    if (controller !== this._controller || this._state !== Timeline.TimelinePanel.State.Recording)
       return;
-    this._recordingPageReload = false;
     this._stopRecording();
   }