IndexedDB: Remove prefetching method stubs from Blink

IndexedDB: Remove prefetching method stubs from Blink

Prefetching is implemented entirely in Chromium (apart from the 
postSuccess... side of things); now that the backend is moved,
various interfaces can be simplified and stubs removed.

BUG=234278
R=abarth@chromium.org, alecflett@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=152153

[jsbell, 2013-06-10 16:47:33]

alecflett@, jamesr@ - please take a look?

All code deletion.

[alecflett, 2013-06-10 16:50:11]

On 2013/06/10 16:47:33, jsbell wrote:
> alecflett@, jamesr@ - please take a look?
> 
> All code deletion.

lgtm

[abarth-chromium, 2013-06-10 17:34:48]

LGTM2

[commit-bot: I haz the power, 2013-06-10 17:35:25]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/jsbell@chromium.org/16320013/2001

[commit-bot: I haz the power, 2013-06-10 20:06:40]

Retried try job too often on win_layout_rel for step(s) webkit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_layout...

[jsbell, 2013-06-10 20:11:52]

Committed patchset #2 manually as r152153 (presubmit successful).