Refactor ZygoteInit to support a WebView-specific zygote.

This is a non-functional change that separates out functionality
that should be shared between the system zygote and the WebView
zygote from that which is system zygote specific.

* Move MethodAndArgsCaller to Zygote.
* Split out server socket functions into ZygoteServer.
* Add a new (stub, for now) WebViewZygoteInit class.

Bug: 22084679
Bug: 21643067
(cherry picked from commit ba816e0c9efd8cd2aeef618a819a2ad46b742f87)
(cherry picked from commit b9679dc1fad508a001e30a941148e1bdc3fe953f)

Change-Id: Iefdb0784dd08ac09a23aafe18663c13dce421775
7 files changed