Improve dom_perf expectations.
Improve dom_perf expectations.

This improved quite a bit recently, but it's not obvious to me why:
http://build.chromium.org/f/chromium/perf/vista-release-dual-core/dom_perf/report.html?history=150&rev=116185
http://build.chromium.org/f/chromium/perf/linux-release/dom_perf/report.html?history=150&rev=116195

probably r116084: wk roll 103871:103889

BUG=none
TEST=none
Review URL: http://codereview.chromium.org/9071016

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@116205 0039d316-1c4b-4281-b951-d872f2087c98

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