RemoteMacViews: Fix crash when fullscreening PWA windows

This CL adds a simple null check before accessing the bridge_impl()
to check whether a fullscreen transition is in progress. This fixes
PWA windows crashing the browser process when the user fullscreens
the window.

bridge_impl() will be null for cross process PWA windows. Plumbing
the call through via bridge() doesn't fix the fullscreen behaviour.
Opened bug to track behavioural issue: https://crbug.com/915110

Bug: 913337
Change-Id: I060bcae3dfced784353a0210b2464d3749969dff
Reviewed-on: https://chromium-review.googlesource.com/c/1375299
Reviewed-by: ccameron <ccameron@chromium.org>
Commit-Queue: Alan Cutter <alancutter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#616603}
1 file changed