Fix a DCHECK in the MetricsService implementation.
Fix a DCHECK in the MetricsService implementation.

I had mistakenly thought that content::URLFetcher::RESPONSE_CODE_INVALID could never be returned in a valid flow; but it can indeed be returned if, e.g., the server is down (or doesn't even exist).  Hence, we need a different sentinel value for the "response code uninitialized" case.

BUG=119894
TEST=Run a Debug build of Chromium on Windows with metrics logging enabled, make sure this DCHECK is not reached.


Review URL: http://codereview.chromium.org/9839085

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@129159 0039d316-1c4b-4281-b951-d872f2087c98

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