Speculative fix for crbug.com/1102668

We appear to crash in HTMLTrackElement::CanLoadUrl if GetExecutionContext()
returns nullptr, so early-exit in that case.

Bug: 1102668
Change-Id: I43f0008eefe5d12b63d69c42d0fd341fe0e2f2eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2284390
Commit-Queue: Kentaro Hara <haraken@chromium.org>
Auto-Submit: Nate Chapin <japhet@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786091}

third_party/blink/renderer/core/html/track/html_track_element.cc

@@ -220,7 +220,7 @@ void HTMLTrackElement::LoadTimerFired(TimerBase*) {
 
 bool HTMLTrackElement::CanLoadUrl(const KURL& url) {
   HTMLMediaElement* parent = MediaElement();
-  if (!parent)
+  if (!parent || !GetExecutionContext())
     return false;
 
   if (url.IsEmpty())