Update performance expectations for linux-release-lowmem

Update expectations.

linux-release-lowmem/moz: http://build.chromium.org/f/chromium/perf/linux-release-lowmem/moz/report.html?history=250&rev=137961
linux-release-lowmem/intl1: http://build.chromium.org/f/chromium/perf/linux-release-lowmem/intl1/report.html?history=150&rev=137961
linux-release-lowmem/database/*: http://build.chromium.org/f/chromium/perf/linux-release-lowmem/database/report.html?history=150&rev=137961&graph=select-readtransactions-read-results
linux-release-lowmem/v8_benchmark: http://build.chromium.org/f/chromium/perf/linux-release-lowmem/v8_benchmark/report.html?history=150&rev=137961

TBR=cmp
BUG=128645, 121574
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=137974

[cmp, 2012-05-21 22:10:39]

lgtm