IndexedDB: Array-type keypaths should not be returned as DOMStringLists

IndexedDB: Array-type keypaths should not be returned as DOMStringLists

Spec (and Gecko) return plain Array objects when inspecting key paths
via an IDBIndex's keyPath attributed. This was never specified or
documented to return a DOMStringList. It looks like it fell out of
Blink's use of an IDBAny variant type for IDL 'any', and was not
changed when keypath-specific bindings code was added.

BUG=499998
R=philipj@opera.com

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197064

[jsbell, 2015-06-12 20:57:33]

philipj@ - please take a look?

I'm reasonably confident that no-one will be using the DSL methods on instances
returned via this mechanism, since it was never documented and no other browser
had this behavior. We could do further instrumentation as in crrev.com/966843002
to measure and make absolutely sure.

[philipj_slow, 2015-06-12 21:30:09]

LGTM, this seems low risk given Gecko's behavior and general obscurity. It would
need a specific use counter to not be mixed up with other DOMStringList cases,
and seems quite excessive.

[jsbell, 2015-06-12 22:06:13]

The CQ bit was checked by jsbell@chromium.org

[commit-bot: I haz the power, 2015-06-12 22:06:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1184503003/1

[commit-bot: I haz the power, 2015-06-12 22:17:46]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197064

[haraken, 2015-06-13 00:42:32]

bindings/ LGTM