Fix Mac tree bustage
Fix Mac tree bustage

Remove overly aggressive DCHECK() which was tripping in 
HISTOGRAM_ENUMERATION on the mac.

BUG=31206
TBR=ramana.tenneti
Review URL: http://codereview.chromium.org/519006

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@35296 0039d316-1c4b-4281-b951-d872f2087c98

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