Use v8::Context::kDebugIdIndex instead of hardwired constant in gin

Use v8::Context::kDebugIdIndex instead of hardwired constant in gin

BUG=466631
Committed: https://crrev.com/ea4636ec3229685a87244d76c6ab144ee86a801c
Cr-Commit-Position: refs/heads/master@{#321534}

[yurys, 2015-03-19 08:18:54]

yurys@chromium.org changed reviewers:
+ jochen@chromium.org

[jochen (gone - plz use gerrit), 2015-03-19 08:30:44]

On 2015/03/19 at 08:18:54, yurys wrote:
> 

What if the constant was eg 42, would we allocate enough internal fields for a
new context?

[yurys, 2015-03-19 09:09:28]

On 2015/03/19 08:30:44, jochen (slow) wrote:
> On 2015/03/19 at 08:18:54, yurys wrote:
> > 
> 
> What if the constant was eg 42, would we allocate enough internal fields for a
> new context?

kDebugIdIndex is essentially last (and only) embedder data index reserved by v8
for its needs so if the constant was 42 that would mean that v8 reserved first
43 indexes for its needs and would have to allocate them. We may add an alias
like v8::Context::kLastReservedEmbedderDataIndex and use it instead of
kDebugIdIndex here. Though as there is only one reserved index at the moment and
it hasn't changed for long enough I'm not sure if it is worthwhile. WDYT?

[jochen (gone - plz use gerrit), 2015-03-19 09:41:17]

k, probably not worthwhile

lgtm like this

[yurys, 2015-03-20 06:43:59]

The CQ bit was checked by yurys@chromium.org

[commit-bot: I haz the power, 2015-03-20 06:44:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1011553003/1

[commit-bot: I haz the power, 2015-03-20 07:13:18]

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

[commit-bot: I haz the power, 2015-03-20 07:13:19]

Try jobs failed on following builders:
  mac_chromium_rel_ng on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)

[yurys, 2015-03-20 07:32:10]

The CQ bit was checked by yurys@chromium.org

[commit-bot: I haz the power, 2015-03-20 07:32:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1011553003/1

[commit-bot: I haz the power, 2015-03-20 08:54:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-20 08:55:01]

Patchset 1 (id:??) landed as
https://crrev.com/ea4636ec3229685a87244d76c6ab144ee86a801c
Cr-Commit-Position: refs/heads/master@{#321534}