test: Replace _TEST_CASE_ with _TEST_SUITE_ in /ios.

Googletest is (at last) converging with industry-standard terminology
[1]. We previously called test suites "test cases", which was rather
confusing for folks coming from any other testing framework.

Chrome now has a googletest version that supports _TEST_SUITE_ macros
instead of _TEST_CASE_, so this CL cleans up some of the outdated usage.

[1] https://github.com/google/googletest/blob/master/googletest/docs/primer.md#beware-of-the-nomenclature

R=eugenebut@chromium.org

Bug: 925652
Change-Id: Ia05667d07a48f1e04d69efc683c2e4c5e4826a4b
Reviewed-on: https://chromium-review.googlesource.com/c/1437353
Commit-Queue: Eugene But <eugenebut@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Auto-Submit: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631793}
9 files changed