Some cleanups in the code that posts results to service clients.

Some cleanups in the code that posts results to service clients.

- Remove the notion of event families and masks.  This wasn't really used.

- Change "response" to "result" in our response map to be more json-rpc-like.

- Pass events to the service isolate as Strings.

- Add more type declarations around raw data (Uint8List) responses.

BUG=
R=johnmccutchan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=45034

[turnidge, 2015-04-09 20:42:01]

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

[turnidge, 2015-04-09 20:42:02]

TBR=cutch

This is a duplicate of an earlier cl that you reviewed... I switched machines so
it is a new code review.

[Cutch, 2015-04-09 20:47:23]

lgtm

[turnidge, 2015-04-09 21:08:52]

Committed patchset #2 (id:20001) manually as 45034 (presubmit successful).