Add debug only counters to profiler

Add debug only counters to profiler

- [x] Count the reasons why we don't walk the stack.
- [x] Count the reasons why we only sample a single frame.
- [x] Count the stack walkers used.

These counters are returned as part of the profile over the vm-service and can be used to debug profiler failures in the future.

R=fschneider@google.com

Committed: https://github.com/dart-lang/sdk/commit/a6e2a7f0cd53c45fab21245f482b2b68a8d07e82

[Cutch, 2016-07-28 01:07:48]

Description was changed from

==========
Add debug only counters to profiler

BUG=
==========

to

==========
Add debug only counters to profiler

BUG=
==========

[Cutch, 2016-07-28 01:07:48]

johnmccutchan@google.com changed reviewers:
+ fschneider@google.com, rmacnak@google.com

[Cutch, 2016-07-28 01:08:46]

Description was changed from

==========
Add debug only counters to profiler

BUG=
==========

to

==========
Add debug only counters to profiler

- [x] Count the reasons why we don't walk the stack.
- [x] Count the reasons why we only sample a single frame.
- [x] Count the stack walkers used.

These counters are returned as part of the profile over the vm-service and can
be used to debug profiler failures in the future.
==========

[Florian Schneider, 2016-07-28 16:53:45]

Lgtm. Thanks!

[Cutch, 2016-07-28 16:56:18]

Description was changed from

==========
Add debug only counters to profiler

- [x] Count the reasons why we don't walk the stack.
- [x] Count the reasons why we only sample a single frame.
- [x] Count the stack walkers used.

These counters are returned as part of the profile over the vm-service and can
be used to debug profiler failures in the future.
==========

to

==========
Add debug only counters to profiler

- [x] Count the reasons why we don't walk the stack.
- [x] Count the reasons why we only sample a single frame.
- [x] Count the stack walkers used.

These counters are returned as part of the profile over the vm-service and can
be used to debug profiler failures in the future.

R=fschneider@google.com

Committed:
https://github.com/dart-lang/sdk/commit/a6e2a7f0cd53c45fab21245f482b2b68a8d07e82
==========

[Cutch, 2016-07-28 16:56:20]

Committed patchset #1 (id:1) manually as
a6e2a7f0cd53c45fab21245f482b2b68a8d07e82 (presubmit successful).