Add fake for InstanceIDWithSubtype.java, in order to re-use unit test

Adds FakeInstanceIDWithSubtype, which closely mimics the behavior of the
Google Play Services InstanceID class (but doesn't make network requests
of course).

Hence InstanceIDDriverTest (instance_id_driver_unittest.cc) is enabled
on Android, verifying that the behavior there is the same as the
existing behavior that it is testing on desktop.

Part of a series of patches:
1. https://codereview.chromium.org/1832833002 adds InstanceIDWithSubtype
2. https://codereview.chromium.org/1830983002 adds JNI bindings
3. this patch
4. https://codereview.chromium.org/1899753002 fixes strict mode violations
5. https://codereview.chromium.org/1854093002 enables InstanceID by default
6. https://codereview.chromium.org/1851423003 switches Push to InstanceIDs

BUG=589461

Review URL: https://codereview.chromium.org/1829023002

Cr-Commit-Position: refs/heads/master@{#389128}
14 files changed