Move shell_util's RegistryEntry class into a separate file.

Makes shell_util more modular and breaks it up a bit. RegistryEntry is a
generally useful API.

BUG=419972

Review URL: https://codereview.chromium.org/623903002

Cr-Commit-Position: refs/heads/master@{#362923}
5 files changed