Reland: Debugger: deduplicate shared function info when setting script break points.

Revert of Revert of Debugger: deduplicate shared function info when setting script break points. (patchset #1 id:1 of https://codereview.chromium.org/999273003/)

Reason for revert:
Reland since the failure has been fixed in https://codereview.chromium.org/1035523005/

Original issue's description:
> Revert of Debugger: deduplicate shared function info when setting script break points. (patchset #4 id:60001 of https://codereview.chromium.org/998253005/)
>
> Reason for revert:
> Code caching failures.
>
> Original issue's description:
> > Debugger: deduplicate shared function info when setting script break points.
> >
> > Also fix Debug.showBreakPoints for multiple break points at the same location.
> >
> > BUG=v8:3960
> > LOG=N
> >
> > Committed: https://crrev.com/73b17a71a22564c0b66d9aa7c00948c748f5b290
> > Cr-Commit-Position: refs/heads/master@{#27444}
>
> TBR=mstarzinger@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=v8:3960
>
> Committed: https://crrev.com/9b29d008dfcc00bf56be8040add1d2c5e404673b
> Cr-Commit-Position: refs/heads/master@{#27448}

TBR=mstarzinger@chromium.org
BUG=v8:3960
LOG=N

Committed: https://crrev.com/69383d6366891c8b1eb2240af55b3ef40628efa6
Cr-Commit-Position: refs/heads/master@{#27472}

[Yang, 2015-03-26 09:57:36]

Created Revert of Revert of Debugger: deduplicate shared function info when
setting script break points.

[Yang, 2015-03-26 09:58:04]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-03-26 09:58:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1037013002/1

[commit-bot: I haz the power, 2015-03-26 09:59:42]

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

[commit-bot: I haz the power, 2015-03-26 09:59:43]

Try jobs failed on following builders:
  v8_linux_arm64_rel on tryserver.v8 (JOB_FAILED,
http://build.chromium.org/p/tryserver.v8/builders/v8_linux_arm64_rel/builds/4248)

[Yang, 2015-03-26 10:21:35]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-03-26 10:21:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1037013002/210001

[commit-bot: I haz the power, 2015-03-26 10:43:41]

Committed patchset #2 (id:210001)

[commit-bot: I haz the power, 2015-03-26 10:44:00]

Patchset 2 (id:??) landed as
https://crrev.com/69383d6366891c8b1eb2240af55b3ef40628efa6
Cr-Commit-Position: refs/heads/master@{#27472}