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This moves it out of ppapi/native_client/tests/, which is a directory
of deprecated things.

I've changed #include ordering to pass the presubmit checks, and also
removed some unused #includes of
native_client/src/shared/platform/nacl_check.h.

BUG=154400
TEST=browser_tests

Review URL: https://codereview.chromium.org/1815113002

Cr-Commit-Position: refs/heads/master@{#382012}