Add Manifest struct converters

This is a part of moving manifest implementation to blink and
the precursor patch before moving content::ManifestManager to
blink and will be used for RequestManifestCallback in
blink::ManifestManager to convert from blink::Manifest to
blink::mojom::blink::ManifestPtr.

Bug: 704441
Change-Id: Iafb5d052f927d6200f7780c5d3537f2120b74ab7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1575258
Commit-Queue: Miyoung Shin <myid.shin@igalia.com>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653056}
3 files changed