Serializer: simplify external reference encoding.

Serializer: simplify external reference encoding.

External references are encoded as a tuple of type and ID. This
requires both the external reference encode and the decoder to
create a mapping between the encoding and the external reference
table index.

Instead, we simply use the external reference table index as
encoding.

We now also assume that there are no duplicate entries. Existing
duplicates have been removed in this change.

R=vogelheim@chromium.org

Committed: https://crrev.com/a8e82da6a57ea00414dbf6a3f4341c08c5ed1705
Cr-Commit-Position: refs/heads/master@{#27033}

[Erik Corry, 2015-03-05 10:44:18]

erik.corry@gmail.com changed reviewers:
+ erik.corry@gmail.com

[Erik Corry, 2015-03-05 10:44:19]

LGTM, but

This is going to be very hard to debug if someone adds an external reference
like the counter, which can be either present or absent depending on
configuration.  You fixed that one in the CL, but when new ones arise, it will
silently wire up all the external references after the extra one wrong. It might
help to at least store the number of external references in the snapshot and
compare with the number in the equivalent table in the deserializing VM.

[Yang, 2015-03-05 11:35:16]

On 2015/03/05 10:44:19, Erik Corry wrote:
> LGTM, but
> 
> This is going to be very hard to debug if someone adds an external reference
> like the counter, which can be either present or absent depending on
> configuration.  You fixed that one in the CL, but when new ones arise, it will
> silently wire up all the external references after the extra one wrong. It
might
> help to at least store the number of external references in the snapshot and
> compare with the number in the equivalent table in the deserializing VM.

When using incompatible snapshots, I expect the version hashes to mismatch
first.

[Yang, 2015-03-05 11:35:49]

On 2015/03/05 11:35:16, Yang wrote:
> On 2015/03/05 10:44:19, Erik Corry wrote:
> > LGTM, but
> > 
> > This is going to be very hard to debug if someone adds an external reference
> > like the counter, which can be either present or absent depending on
> > configuration.  You fixed that one in the CL, but when new ones arise, it
will
> > silently wire up all the external references after the extra one wrong. It
> might
> > help to at least store the number of external references in the snapshot and
> > compare with the number in the equivalent table in the deserializing VM.
> 
> When using incompatible snapshots, I expect the version hashes to mismatch
> first.

But I do see your point. Will add a field to the header for this

[Yang, 2015-03-05 13:46:31]

On 2015/03/05 11:35:49, Yang wrote:
> On 2015/03/05 11:35:16, Yang wrote:
> > On 2015/03/05 10:44:19, Erik Corry wrote:
> > > LGTM, but
> > > 
> > > This is going to be very hard to debug if someone adds an external
reference
> > > like the counter, which can be either present or absent depending on
> > > configuration.  You fixed that one in the CL, but when new ones arise, it
> will
> > > silently wire up all the external references after the extra one wrong. It
> > might
> > > help to at least store the number of external references in the snapshot
and
> > > compare with the number in the equivalent table in the deserializing VM.
> > 
> > When using incompatible snapshots, I expect the version hashes to mismatch
> > first.
> 
> But I do see your point. Will add a field to the header for this

done.

[Yang, 2015-03-06 07:58:08]

The CQ bit was checked by yangguo@chromium.org

[Yang, 2015-03-06 07:58:09]

The patchset sent to the CQ was uploaded after l-g-t-m from erik.corry@gmail.com
Link to the patchset: https://codereview.chromium.org/982773003/#ps110001
(title: "rebase")

[commit-bot: I haz the power, 2015-03-06 07:59:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/982773003/110001

[commit-bot: I haz the power, 2015-03-06 07:59:57]

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

[commit-bot: I haz the power, 2015-03-06 07:59:57]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer,
_not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Sven Panne, 2015-03-06 08:13:12]

svenpanne@chromium.org changed reviewers:
+ svenpanne@chromium.org

[Sven Panne, 2015-03-06 08:13:12]

LGTM (mostly rubberstamped, I need the simplification in serialize.cc :-)

[Yang, 2015-03-06 08:13:26]

The CQ bit was checked by yangguo@chromium.org

[commit-bot: I haz the power, 2015-03-06 08:13:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/982773003/110001

[commit-bot: I haz the power, 2015-03-06 08:15:08]

Committed patchset #7 (id:110001)

[commit-bot: I haz the power, 2015-03-06 08:15:36]

Patchset 7 (id:??) landed as
https://crrev.com/a8e82da6a57ea00414dbf6a3f4341c08c5ed1705
Cr-Commit-Position: refs/heads/master@{#27033}