GitLab

This is a follow-up CL of r314351.

Currently this is invoked from PermissionContextBase. Since this is for
protected media identifier only, it's better to put it in
ProtectedMediaIdentifierPermissionContext.

Also included in this fix:
- Pass |requesting_origin| to PlatformVerificationDialog::ShowDialog().
  Currently we are using the origin of the GetLastCommittedURL(), which is
  wrong.
- Add ProtectedMediaIdentifierPermissionContext::CancelPermissionRequest() so
  that we can cancel the prompt and drop the callback properly. Otherwise, this
  will cause a DCHECK in PermissionServiceImp when closing the browser while the
  prompt is shown.

BUG=446263
TEST=Manually tested various cases.

Review URL: https://codereview.chromium.org/881983003

Cr-Commit-Position: refs/heads/master@{#314924}