move context id constant to AnalysisServer

move context id constant to AnalysisServer

BUG=
R=brianwilkerson@google.com, paulberry@google.com

Committed: https://code.google.com/p/dart/source/detail?r=36263

[danrubel, 2014-05-16 15:30:22]

Move constant to AnalysisServer so that it can be used in that class and
elsewhere without adding a dependence on ServerDomainHandler.

[Paul Berry, 2014-05-16 15:38:13]

lgtm

I'm not sure I completely understand the benefit, though.  I thought the idea
was that ContextDomainHandler was responsible for reading the contextId out of
the incoming request message and using that to look up the AnalysisContext (via
getAnalysisContext).  So why are we going to need to use the constant from
AnalysisServer and elsewhere?

[Brian Wilkerson, 2014-05-16 15:53:34]

LGTM

> So why are we going to need to use the constant from AnalysisServer and
elsewhere?

Almost every domain (other than 'server') uses a context id parameter in the
request.

[danrubel, 2014-05-16 17:44:31]

Committed patchset #2 manually as r36263 (presubmit successful).