Add deprecation message for AppCache in insecure contexts

This adds a deprecation messages for uses of the manifest attribute or
use of the AppCache API in insecure contexts. Adds LayoutTests as well
to confirm warning messages. Additionally, adds counts and RAPPOR stats
to track usage.

BUG=588931

Review URL: https://codereview.chromium.org/1723353002

Cr-Commit-Position: refs/heads/master@{#377463}
13 files changed