Remove disk_cache::BackendImpl::OpenPrevEntry() and all users.

Remove disk_cache::BackendImpl::OpenPrevEntry() and all users.

While working on https://codereview.chromium.org/542733002/ to fix
issue 410276, a question came up about how important OpenPrevEntry was
to maintain; it made that CL more complex and for what users?

It turns out, it's not really used. See
https://groups.google.com/a/chromium.org/forum/#!topic/net-dev/wlMR_zNJ85k
for a discussion.

Let's remove it and save ourselves some headaches.

R=clamy@chromium.org
BUG=410276
Committed: https://crrev.com/1d6a91d497fccffbc7b26be4d9c6025a4e42a3dd
Cr-Commit-Position: refs/heads/master@{#293593}

[gavinp, 2014-09-05 02:06:06]

clamy: as you suggested, here we are! This change is discussed in
https://groups.google.com/a/chromium.org/forum/#!topic/net-dev/wlMR_zNJ85k as
well.

[clamy, 2014-09-05 14:47:40]

Thanks! Removing unused code is nice :).

https://chromiumcodereview.appspot.com/547513002/diff/20001/net/disk_cache/bl...
File net/disk_cache/blockfile/backend_impl_v3.cc (left):

https://chromiumcodereview.appspot.com/547513002/diff/20001/net/disk_cache/bl...
net/disk_cache/blockfile/backend_impl_v3.cc:966: int
BackendImplV3::OpenFollowingEntry(bool forward, void** iter,
I am a bit confused about this function. The comments hint that it is used for
OpenNextEntry, but OpenNextEntry is not implemented. What is the status of the
backend v3?

[gavinp, 2014-09-05 15:10:51]

On 2014/09/05 14:47:40, clamy wrote:
> Thanks! Removing unused code is nice :).
> 
>
https://chromiumcodereview.appspot.com/547513002/diff/20001/net/disk_cache/bl...
> File net/disk_cache/blockfile/backend_impl_v3.cc (left):
> 
>
https://chromiumcodereview.appspot.com/547513002/diff/20001/net/disk_cache/bl...
> net/disk_cache/blockfile/backend_impl_v3.cc:966: int
> BackendImplV3::OpenFollowingEntry(bool forward, void** iter,
> I am a bit confused about this function. The comments hint that it is used for
> OpenNextEntry, but OpenNextEntry is not implemented. What is the status of the
> backend v3?

It's not under active development, and it doesn't yet work. That function was
cut and paste from v2, presumably to be one day updated, but it had no callers,
so rather than update it (removing forward), I thought just removing it was
best.

[clamy, 2014-09-05 15:15:44]

Ok, rslgtm.

[clamy, 2014-09-05 15:16:22]

On 2014/09/05 15:15:44, clamy wrote:
> Ok, rslgtm.

lgtm (seems it did not work above).

[gavinp, 2014-09-05 18:22:19]

The CQ bit was checked by gavinp@chromium.org

[commit-bot: I haz the power, 2014-09-05 18:22:51]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/gavinp@chromium.org/547513002/20001

[commit-bot: I haz the power, 2014-09-05 19:18:33]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-05 19:18:34]

Try jobs failed on following builders:
  android_clang_dbg_recipe on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_clang_d...)

[gavinp, 2014-09-05 23:03:19]

The CQ bit was checked by gavinp@chromium.org

[commit-bot: I haz the power, 2014-09-05 23:04:35]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/gavinp@chromium.org/547513002/20001

[commit-bot: I haz the power, 2014-09-05 23:33:19]

Committed patchset #2 (id:20001) as aa411cf597e9f6c1e13f2030f715e71c51f973c9

[commit-bot: I haz the power, 2014-09-10 03:41:54]

Patchset 2 (id:??) landed as
https://crrev.com/1d6a91d497fccffbc7b26be4d9c6025a4e42a3dd
Cr-Commit-Position: refs/heads/master@{#293593}