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This is a reland of a2a4e75d with a
work-around for cronet_tests' sharing libbase.so with libcronet.so in
component builds.

- Move some APIs off of base::TestSuite, that we unnecessarily public.
- Rename the various internal TestEventListeners to express purpose.
- Add CheckForLeakedGlobals check, and DisableCheckForLeakedGlobals API.
  The latter is called by the content::ContentTestSuiteBase, since the
  various browser- and ui-tests running under that suite base run more
  like the browser itself, and so are expected to let global singletons
  leak.

If tests fail or flake due to this patch, then this indicates that the
test is actually leaking global state that may break other tests if they
happen to run in the same process, leading to hard-to-diagnose flakes.

There are two main failure cases:
If the test directly or indirectly uses TaskScheduler, but does not
create a ScopedTaskEnvironment, then please add one to the test, or to
the test base-class, as appropriate, to fix it.
If the test suite cannot be fixed in this way then please add a call to
DisableCheckForLeakedGlobals(), with a comment linking to a bug for the
issue.

TBR: gab, sky, mef
Bug: 875486, 877355, 744567
Change-Id: Iaea38d24ede271c248a3abb0b3f7ee931c2538f5
Reviewed-on: https://chromium-review.googlesource.com/1187783Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586065}