IndexedDB: Consume SSV wire format version from Blink public headers

IndexedDB writes the "wire format version" for serialized
data into the database metadata to detect the case where
a user reverts to an older version of the browser and
data "from the future" will not be understood. Detecting
this early lets us fail the open, rather than later
mysterious inconsistency errors. When the back-end was in
Blink the value could be grabbed directly from the
SerializedScriptValue class. Now it is exposed via headers.

BUG=299125

Review URL: https://codereview.chromium.org/24904002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226338 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226338