Begin divorcing requesting notification permissions from the presenter.

Requesting permission to be able to display Web Notifications is the only
functionality which will be routed through a WebFrame, all other operations
(including checking for permission) will go through Platform. This patch
introduces the still unused APIs, allowing them to be implemented in
Chromium land.

Furthermore, amend the WebNotificationPermissionCallback interface to
allow the actual permission to be passed in to permissionRequestComplete.
Currently we do another renderer<-->browser round-trip through a sync
IPC, which can easily be avoided by passing it in.

BUG=392187

Review URL: https://codereview.chromium.org/372313002

git-svn-id: svn://svn.chromium.org/blink/trunk@177749 bbb929c8-8fbe-4397-9dbb-9b2b20218538