Adjust variance for linux perf test expectations.
Adjust variance for linux perf test expectations.

This patch should cause the linux perf morejs and
startup tests to go green.

BUG=18597
TEST=linux perf morejs and startup perf tests go green
Review URL: http://codereview.chromium.org/189008

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@25260 0039d316-1c4b-4281-b951-d872f2087c98

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