test: Replace _TEST_CASE_ with _TEST_SUITE_ in /ios/chrome/browser/metrics.

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 googltest 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instead of _TEST_CASE_, so this CL cleans up some of the outdated usage.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

This CL was uploaded by git cl split.

R=olivierrobin@chromium.org

Bug: 925652
Change-Id: I0dbcf574eaa0c466dfcd3db3c083fac7ef9ab53c
Reviewed-on: https://chromium-review.googlesource.com/c/1438366
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626480}

ios/chrome/browser/metrics/mobile_session_shutdown_metrics_provider_unittest.mm

@@ -175,6 +175,6 @@ TEST_P(MobileSessionShutdownMetricsProviderTest, ProvideStabilityMetrics) {
                                       expected_buckets[GetParam()], 1);
 }
 
-INSTANTIATE_TEST_CASE_P(/* No InstantiationName */,
+INSTANTIATE_TEST_SUITE_P(/* No InstantiationName */,
                          MobileSessionShutdownMetricsProviderTest,
                          testing::Range(0, 32));