IDL: Add support for serializer definitions

IDL: Add support for serializer definitions

A serializer definition is output as a 'Serializer' production, with
either no children, an 'Operation' child, or a 'Map'/'List' child. The
production has an attribute named 'ATTRIBUTE' in the

  serializer = identifier;

form (and no children), and the 'Map'/'List' productions have attributes
named 'GETTER', 'INHERIT' and 'ATTRIBUTES', where the latter is a list of
the attributes named in the definition.

BUG=469650
Committed: https://crrev.com/577bccbad01ca22a55df7d6c828459e39616d8fd
Cr-Commit-Position: refs/heads/master@{#321780}

[Jens Widell, 2015-03-23 11:42:55]

jl@opera.com changed reviewers:
+ bashi@chromium.org, haraken@chromium.org

[Jens Widell, 2015-03-23 11:42:56]

PTAL

[haraken, 2015-03-23 13:30:59]

LGTM

[Jens Widell, 2015-03-23 14:41:46]

The CQ bit was checked by jl@opera.com

[commit-bot: I haz the power, 2015-03-23 14:42:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1031593003/60001

[commit-bot: I haz the power, 2015-03-23 15:43:46]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-03-23 15:44:36]

Patchset 4 (id:??) landed as
https://crrev.com/577bccbad01ca22a55df7d6c828459e39616d8fd
Cr-Commit-Position: refs/heads/master@{#321780}

[bashi, 2015-03-24 00:22:59]

LGTM