Create initial split of //components/signin test_support target

//components/signin/core/browser contains three different types of code:

1. Code that forms the guts of IdentityManager and will form the guts of
the Identity Service implementation (e.g., SigninManager).

2. Code that will be clients of IdentityManager (e.g., SigninTracker).

3. Code that will be used on both sides (e.g., AccountInfo).

Currently, the test support for all of these is naturally grouped in the
same GN target, since there was never any distinction between them.
However, we need to separate this test support in GN now, as the test
support for IdentityManager should depend only on 1 and 3 (and their
associated test support).

This CL performs an initial split, via the following process:

- Moved fake_signin_manager.*, fake_profile_oauth2_token_service.*, and
  fake_gaia_cookie_manager_service.* into a new "test_support_internals"
  target that the existing target now depends on.
- Kept moving in code (and adding dependencies as needed) until
  "gn check" no longer complained about the "test_support_internals"
  target including code that wasn't in any dependencies.

This CL also modifies //services/identity/public/cpp:test_support to
depend only on //components/signin/core/browser:internals_test_support;
this change is is the concrete benefit from doing the split.

Finally, this CL strips both the test_support_internals and the
test_support target down to the dependencies that they actually need;
this change necessitated added some missing direct dependencies to
other targets.

Bug: 901859
Change-Id: I0ac61f69c0c897d97b570c16d06f0e4f5f99d037
Reviewed-on: https://chromium-review.googlesource.com/c/1319669
Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606046}
5 files changed