Allow observatory to distinguish between user-level and vm-level types.

Allow observatory to distinguish between user-level and vm-level types.

Currently the 'type' property always encodes a vm-specific type.  In
the future 'type' will specify a user-level (Dart-ish) type and
'vmType' will (optionally) specify a vm-specific type if it is
different.  This will allow an application like a debugger (for
example) to ignore the specifics of the vm-internal Instance hierarchy
while still providing this information for applications like
Observatory, which want to know everything.

So, in this change, we prepare Observatory to receive both 'type' and
'vmType' properties.

Specifics:

- replace 'serviceType' on ServiceObject with 'type' and 'vmType'.
- replace uses of serviceType with type or vmType as appropriate.
- fix a couple of stray bugs I found ('user_name', etc.)

BUG=
R=johnmccutchan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=39705

[turnidge, 2014-08-28 19:48:18]

turnidge@google.com changed reviewers:
+ johnmccutchan@google.com

[Cutch, 2014-08-29 16:33:52]

lgtm

[turnidge, 2014-08-29 17:17:54]

Committed patchset #2 (id:20001) manually as 39705 (presubmit successful).