Remove CHECK for routing id.

This CHECK was introduced to help diagnose why we are seeing failures during child frame creation. We now understand part of the cases, so this CHECK is no longer needed.

BUG=336014

Review URL: https://codereview.chromium.org/141003011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@246261 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 246261