GitLab

There is a crash in ProcessNavigationDecision, accessing an almost null
pointer. From disassembly inspection this is likely accessing the vtable
which means the Throttle got destroyed

Likely code path
- start navigation
- send throttle decision request
- navigation cancelled for some reason, throttle destroyed
- reply arrives

There was no code path to handle nulling the throttle if it got destroyed.
This CL adds this path and a second one to prevent a future
webview dtor -> throttle dtor crash

Bug: b/148126060
Test: None, can't repro crash
Change-Id: I4cb4d5720c114c97d49bae95f0768da0d8c025b1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2023048Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Commit-Queue: Albert Chaulk <achaulk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736039}