Scaffolding for Android implementation of PaymentRequest.

This patch places ServiceRegistryAndroid in content/public/, so Chrome
can register Android-specific services for Mojo. ServiceRegistryAndroid
is a pure virtual interface, implemented by ServiceRegistryAndroidImpl
in content/browser/android/.

The first user of the Android-specific features of Mojo in Chrome is the
PaymentRequest service. This patch adds a skeleton implementation of
this service.

BUG=587995
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation

Review URL: https://codereview.chromium.org/1831173002

Cr-Commit-Position: refs/heads/master@{#385647}
26 files changed