Checkpoint work to get GN builds working on Android.

This fixes enough issues so that we can compile and link some libraries, but
it is not yet a working build.

Work remaining:
- base needs JNI support ('base_jni_headers', etc.)
- we need to figure out what should link and/or be APKs to run the tests
- we need to adjust GN to only build in the host config, not the target config.

R=brettw@chromium.org, cjhopman@chromium.org
TBR=jam
BUG=360936

Review URL: https://codereview.chromium.org/227673008

git-svn-id: https://src.chromium.org/chrome/trunk/src/url@263440 4ff67af0-8c30-449e-8e8b-ad334ec8d88c