Reduce probability of SDCH holdback to 1%
Reduce probability of SDCH holdback to 1%

Anticipating a broader test base, I wanted to reduce the percentage of
uses that were "holdback" (sdch not used when it was available).  This
should reduce the impact on users, and also be sufficient to get
verification statistics from a larger group.

r=huanr
Review URL: http://codereview.chromium.org/118287

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@17700 0039d316-1c4b-4281-b951-d872f2087c98

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