Remove argument on DispatchBeforeUnloadEvent

Sometimes the View is null and we can't get a ChromeClient. Change the
API to take the ChromeClient as a ptr, which also implies the
auto_cancel field.

BUG=907125

Change-Id: I123845c2294ec2c4f155500012280a48ff623c86
Reviewed-on: https://chromium-review.googlesource.com/c/1359056
Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#613721}
4 files changed