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
Committed:
https://crrev.com/1152e786b74c1bbba74af386eb9757f3f8713add
Cr-Commit-Position: refs/heads/master@{#377463}