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This CL extends IdentityTestEnvironment{Profile,ChromeBrowserState}Adaptor
classes with a handful set of APIs needed for identity_apitest.cc, and possibly
some other conversions.

In summary:
- It adds a method that allows setting the testing factories that
 identity::IdentityTestEnvironment requires explicitly on a Profile
 that is passed to it.
- It extends all methods that (in)directly call
  GetIdentityTestEnvironmentFactories with the possibility to use
  or not the "fake URL fetcher" for Gaia's Cookie Manager factory.

BUG=906618

Change-Id: I54985c0743ed0ae2528140fac655fcf1baeb9531
Reviewed-on: https://chromium-review.googlesource.com/c/1346609
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610836}