Check IsContextDestroyed() before calling Abandon()

It is not necessary to call Abandon() if the ExecutionContext is already
destroyed. This is tested in PrerenderingTest.AbandonPrerender.

Bug: 1115764, 1100257
Change-Id: I3f21953c03b2688d0b3760b05a9aabf1ee8ca781
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2355357
Commit-Queue: Yuki Yamada <yukiy@chromium.org>
Reviewed-by: Keishi Hattori <keishi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798541}

third_party/blink/renderer/core/loader/private/prerender_handle.cc

@@ -104,7 +104,7 @@ PrerenderHandle::PrerenderHandle(
 PrerenderHandle::~PrerenderHandle() = default;
 
 void PrerenderHandle::Dispose() {
-  if (remote_handle_.is_bound())
+  if (remote_handle_.is_bound() && !GetExecutionContext()->IsContextDestroyed())
     remote_handle_->Abandon();
   Detach();
 }