Fix hot reload test mode in simdbc by supporting forced slow paths on simdbc

Fix hot reload test mode in simdbc by supporting forced slow paths on simdbc

- [x] Add new SIM DBC byte code: CheckStackAlwaysExit.
- [x] Emit CheckStackAlwaysExit instead of CheckStack when requested.

BUG=
R=rmacnak@google.com

Committed: https://github.com/dart-lang/sdk/commit/8b6f6102062a772d2f9f6bff8c86ac3565fb0cd2

[Cutch, 2016-12-12 21:14:18]

Description was changed from

==========
Fix hot reload test mode in simdbc by supporting forced slow paths on simdbc

- [x] Add new SIM DBC byte code: CheckStackAlwaysExit.
- [x] Emit CheckStackAlwaysExit instead of CheckStack when requested.

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

to

==========
Fix hot reload test mode in simdbc by supporting forced slow paths on simdbc

- [x] Add new SIM DBC byte code: CheckStackAlwaysExit.
- [x] Emit CheckStackAlwaysExit instead of CheckStack when requested.

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

[Cutch, 2016-12-12 21:14:18]

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

[rmacnak, 2016-12-12 22:06:17]

lgtm

[Cutch, 2016-12-12 22:07:27]

Description was changed from

==========
Fix hot reload test mode in simdbc by supporting forced slow paths on simdbc

- [x] Add new SIM DBC byte code: CheckStackAlwaysExit.
- [x] Emit CheckStackAlwaysExit instead of CheckStack when requested.

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

to

==========
Fix hot reload test mode in simdbc by supporting forced slow paths on simdbc

- [x] Add new SIM DBC byte code: CheckStackAlwaysExit.
- [x] Emit CheckStackAlwaysExit instead of CheckStack when requested.

BUG=
R=rmacnak@google.com

Committed:
https://github.com/dart-lang/sdk/commit/8b6f6102062a772d2f9f6bff8c86ac3565fb0cd2
==========

[Cutch, 2016-12-12 22:07:28]

Committed patchset #2 (id:20001) manually as
8b6f6102062a772d2f9f6bff8c86ac3565fb0cd2 (presubmit successful).

[zra, 2016-12-12 22:07:37]

https://codereview.chromium.org/2569013002/diff/20001/runtime/vm/constants_dbc.h
File runtime/vm/constants_dbc.h (right):

https://codereview.chromium.org/2569013002/diff/20001/runtime/vm/constants_db...
runtime/vm/constants_dbc.h:824: V(CheckStackAlwaysExit,            0, ___, ___,
___) \
Maybe CheckStackAlwaysCall?

Please add docs in the comment above.