GitLab

This changes PolicyDecisionStateTracker's destructor to invoke
the state tracker's callback if it hasn't already been invoked.
Destroying the callback without ever invoking it can result in
a WKWebView-provided callback never getting invoked, which
triggers an NSException causing a crash.

In the linked bug, the PolicyDecisionStateTracker is destroyed
as a result of MainFrameUrlQuery::operator= implicitly
releasing its old response_callback, which owns the state
tracker. An alternative fix would be to change that method
to invoke the old response_callback. However, the change made
by this CL is a more general fix for the problem, and should
prevent similar issues in the future.

Bug: 1079471
Change-Id: Ib8782b2278cace0f24692dbe951d498792111095
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2229201
Commit-Queue: Ali Juma <ajuma@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774772}