Fix a variety of service protocol bugs.

Fix a variety of service protocol bugs.

Add documentation for breakpoint.

Fix Instance.pattern documentation.

Fix Instance.bytes documentation.

Add class field for null instances.

Fix documentation of Context and closureContext.

Make getObject return Collected for deleted breakpoints.

Closes #24247
Closes #24249
Closes #24309
Closes #24325
Closes #24326
Closes #24327

BUG=
R=johnmccutchan@google.com

Committed: https://github.com/dart-lang/sdk/commit/b0ca0789be616560c77315ecca290ebcb0735606

[turnidge, 2015-09-11 18:05:08]

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

[Cutch, 2015-09-11 19:22:19]

LGTM with one issue

https://codereview.chromium.org/1341473002/diff/20001/runtime/vm/service.cc
File runtime/vm/service.cc (right):

https://codereview.chromium.org/1341473002/diff/20001/runtime/vm/service.cc#n...
runtime/vm/service.cc:1460: *result = ObjectIdRing::kCollected;
We've been asked for a breakpoint id larger than all ids handed out so far, this
should be kInvalid right?

[turnidge, 2015-09-11 19:29:26]

Committed patchset #3 (id:40001) manually as
b0ca0789be616560c77315ecca290ebcb0735606 (presubmit successful).