Upstream: Extract "WebAPK service" implementation from Chrome APK

Ideally as much WebAPK code as possible can be updated without a new WebAPK
being downloaded from the Chrome server. This CL makes the WebAPK extract
a dex with the "WebAPK service" implementation from the Chrome APK and use
the extracted dex via reflection.

BUG=609122

Review-Url: https://codereview.chromium.org/2011613003
Cr-Commit-Position: refs/heads/master@{#396645}
9 files changed