Fix crash where a pending pointer lock would trigger a CHECK.

This change makes sure that we gracefully handle the case where a
pending pointer lock request is still active while destroying the
RenderWidgetHost.

BUG=655592

Review-Url: https://chromiumcodereview.appspot.com/2437213002
Cr-Commit-Position: refs/heads/master@{#426835}
2 files changed