[Fetch API] Unify stream-reader test expectations.
[Fetch API] Unify stream-reader test expectations.

http/tests/fetch/*/stream-reader*.html fail on Windows or Mac. This CL
unifies cluttered test expectations about these tests.

BUG=472970

Review URL: https://codereview.chromium.org/1120653005

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@194804 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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