Move content::ManifestChangeNotifier and manifest_observer.mojom to blink

This is a part of moving manifest implementation to blink.
This CL moves content::ManifestChangeNotifier and
manifest_observer.mojom to blink and removes
content::ManifestUmaUtil.

Bug: 704441, 919392
Change-Id: I656717f98d2bee7eba2e4728cb35c4515a9303a6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1589477
Commit-Queue: Miyoung Shin <myid.shin@igalia.com>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656728}
29 files changed