Pepper: Manifest ID cleanup.

This removes a bunch of code for managing manifest IDs. Any given instance can
only have one "Json Manifest", as parsed from user-supplied NMF data. Helper
processes (llc and ld) have no corresponding NMF, but do make IRT
open_resource() calls, which eventually manifest in a call to
ManifestResolveKey.

This code should be quite a bit easier to read now, and makes the relationship
between manifest data and instances clearer.

BUG=239656
R=dmichael@chromium.org

Review URL: https://codereview.chromium.org/301013002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@273535 0039d316-1c4b-4281-b951-d872f2087c98
8 files changed