GitLab

Consider the following situation:
- We're running Chromium on Mac
- There's an open context menu for the browser's page

If at this moment we try to close browser programmatically via
DevTools protocol, the browser will not close - it'll hang.

This happens because:
- context menus on mac spawn nested event loops
- `RenderViewContextMenuMacCocoa` is destroyed and doesn't exit the run loop

This patch cleans up context menu when `RenderViewContextMenuMacCocoa` is
destroyed.


Change-Id: Ic2f89806954cb5386d530c6e726386ac7f5d513d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2285520
Commit-Queue: Andrey Lushnikov <lushnikov@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#786119}