IndexedDB: Verify that index id/key vectors are the same length

R=tsepez@chromium.org, ianbeer@chromium.org, inferno@chromium.org
BUG=334274

Review URL: https://codereview.chromium.org/135733003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244786 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244786