Changing a DCHECK to a CHECK in order to catch this error in release builds.
I managed to hit this problem locally by following reproduction steps in
bug 335031. My guess is that this might be causing data corruption and
several so-far unexplained crashes, so I think that a reasonable first step
is to upgrade the DCHECK to a CHECK.

Committing as TBR to get this in asap.

BUG=335031
TBR=agl@chromium.org
NOTRY=True

Review URL: https://codereview.chromium.org/143443002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246036 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246036