I'm trying to fix two separate issues:
1) WebApkApplication currently loads chrome's dex file in all processes and shouldn't
2) Remove the content dependency I introduced in https://codereview.chromium.org/1967733002/

One way to do this would be to have the WebApk define custom classes for privileged/sandboxed renderers and these would either subclass chrome's or possibly more simply, compose an instance. We could then move the code from WebApkApplication into the service class, and forward all methods from the service API to the underlying ChildProcessService. We'd inject the host browser's context at the right place to resolve (2).

The only other change would be in WebappActivity to pass the overriden classname as part of the child process creation params.

wdyt?
Peter, I'm specifically interested in your feedback and wondering whether DexLoader could be reused in lieu of the reflection we currently have