IndexedDB: Remove invalid DCHECK that database name is non-empty

Nothing in the spec - or Blink implementation - precludes empty names
for databases. Remove this bogus DCHECK.

Will add Blink-side layout tests once this lands.

BUG=350133
R=cmumford

Review URL: https://codereview.chromium.org/189413007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255828 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255828