Detect unhandled exceptions in async functions without an awaiter

Detect unhandled exceptions in async functions without an awaiter

- [x] Produce an awaiter stack trace even when there is no awaiter.
- [x] Fix fetching the saved context from Closure.call (fixes --trace_debugger_stacktrace)

Fixes #29200

Example code:

```
main(List<String> args) async {
  var f = new Foo();
  print(f.a.length);
  print('Should not get here');
}

class Foo {
  String a;
}
```

BUG=
R=rmacnak@google.com

Committed: https://github.com/dart-lang/sdk/commit/f0734f99b3c948d53130419c3d5c3666a0578a67

[Cutch, 2017-04-12 14:21:17]

Description was changed from

==========
Detect unhandled exceptions in async functions without an awaiter

- [x] Produce an awaiter stack trace even when there is no awaiter.
- [x] Fix fetching the saved context from Closure.call (fixes
--trace_debugger_stacktrace)

Fixes #29200

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

to

==========
Detect unhandled exceptions in async functions without an awaiter

- [x] Produce an awaiter stack trace even when there is no awaiter.
- [x] Fix fetching the saved context from Closure.call (fixes
--trace_debugger_stacktrace)

Fixes #29200

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

[Cutch, 2017-04-12 14:21:17]

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

[Cutch, 2017-04-12 14:21:47]

Description was changed from

==========
Detect unhandled exceptions in async functions without an awaiter

- [x] Produce an awaiter stack trace even when there is no awaiter.
- [x] Fix fetching the saved context from Closure.call (fixes
--trace_debugger_stacktrace)

Fixes #29200

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

to

==========
Detect unhandled exceptions in async functions without an awaiter

- [x] Produce an awaiter stack trace even when there is no awaiter.
- [x] Fix fetching the saved context from Closure.call (fixes
--trace_debugger_stacktrace)

Fixes #29200

Example code:

```
main(List<String> args) async {
  var f = new Foo();
  print(f.a.length);
  print('Should not get here');
}

class Foo {
  String a;
}
```

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

[rmacnak, 2017-04-12 16:53:04]

lgtm

https://codereview.chromium.org/2815863002/diff/1/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/2815863002/diff/1/runtime/vm/debugger.cc#newc...
runtime/vm/debugger.cc:945: ctx_ ^= Closure::Cast(obj).context();
The parser is uniformly creating a scope entry for the current context, but
closure invocation is the special case where we're setting it up.

ASSERT(function.name() == Symbols::Call());
ASSERT(function.kind() == kInvokeFieldDispatcher);

[Cutch, 2017-04-12 20:15:49]

Description was changed from

==========
Detect unhandled exceptions in async functions without an awaiter

- [x] Produce an awaiter stack trace even when there is no awaiter.
- [x] Fix fetching the saved context from Closure.call (fixes
--trace_debugger_stacktrace)

Fixes #29200

Example code:

```
main(List<String> args) async {
  var f = new Foo();
  print(f.a.length);
  print('Should not get here');
}

class Foo {
  String a;
}
```

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

to

==========
Detect unhandled exceptions in async functions without an awaiter

- [x] Produce an awaiter stack trace even when there is no awaiter.
- [x] Fix fetching the saved context from Closure.call (fixes
--trace_debugger_stacktrace)

Fixes #29200

Example code:

```
main(List<String> args) async {
  var f = new Foo();
  print(f.a.length);
  print('Should not get here');
}

class Foo {
  String a;
}
```

BUG=
R=rmacnak@google.com

Committed:
https://github.com/dart-lang/sdk/commit/f0734f99b3c948d53130419c3d5c3666a0578a67
==========

[Cutch, 2017-04-12 20:15:50]

Committed patchset #2 (id:20001) manually as
f0734f99b3c948d53130419c3d5c3666a0578a67 (presubmit successful).

[siva, 2017-04-13 01:22:58]

https://codereview.chromium.org/2815863002/diff/20001/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/2815863002/diff/20001/runtime/vm/debugger.cc#...
runtime/vm/debugger.cc:942: const Object& obj =
Object::Handle(GetStackVar(var_info.index()));
This handle could be hoisted outside the for loop.

[siva, 2017-04-13 01:30:06]

https://codereview.chromium.org/2815863002/diff/20001/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/2815863002/diff/20001/runtime/vm/debugger.cc#...
runtime/vm/debugger.cc:956: return Context::ZoneHandle(Context::null());
Why is it not ok to use the same ctx_ as above
i.e
ctx ^= Context::null();
return ctx_;

[Cutch, 2017-04-13 14:34:44]

Will TBR changes in another CL.

https://codereview.chromium.org/2815863002/diff/20001/runtime/vm/debugger.cc
File runtime/vm/debugger.cc (right):

https://codereview.chromium.org/2815863002/diff/20001/runtime/vm/debugger.cc#...
runtime/vm/debugger.cc:942: const Object& obj =
Object::Handle(GetStackVar(var_info.index()));
On 2017/04/13 01:22:58, siva wrote:
> This handle could be hoisted outside the for loop.

Done.

https://codereview.chromium.org/2815863002/diff/20001/runtime/vm/debugger.cc#...
runtime/vm/debugger.cc:956: return Context::ZoneHandle(Context::null());
On 2017/04/13 01:30:06, siva wrote:
> Why is it not ok to use the same ctx_ as above
> i.e
> ctx ^= Context::null();
> return ctx_;

Done.

[Cutch, 2017-04-13 14:38:24]

https://codereview.chromium.org/2819523003