Reland: Fix scoping async functions.

Reland: Fix scoping async functions.

This CL fixes several scoping/context issues:
* Do not reuse scopes in SequenceNode_s as they might introduce a new context
  level. In that case we would trigger context allocationg multiple times
  resulting in scope/contexts being out of sync.
* Properly save and restore saved_try_context in try/catch/finally blocks and
  nesting closures. For this we need to keep track of async closures top scopes.

Updated version of https://codereview.chromium.org/520223002/

BUG=
R=hausner@google.com, srdjan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=39810

[Michael Lippautz (Google), 2014-09-03 00:10:44]

mlippautz@google.com changed reviewers:
+ hausner@google.com, srdjan@google.com

[Michael Lippautz (Google), 2014-09-03 00:10:44]

Thanks Srdjan for investigating!

https://codereview.chromium.org/530313002/diff/1/runtime/vm/parser.cc
File runtime/vm/parser.cc (right):

https://codereview.chromium.org/530313002/diff/1/runtime/vm/parser.cc#newcode...
runtime/vm/parser.cc:8595: AstNode* await_preamble = CloseBlock();
the fix is to not use

current_block_->statements->Add(CloseBlock())

as CloseBlock() changes current_block_ and gcc/clang disagree on what to
evaluate first (args or base ptr).

It's also more readable this way :)

[hausner, 2014-09-03 15:40:06]

lgtm

https://codereview.chromium.org/530313002/diff/1/runtime/vm/parser.cc
File runtime/vm/parser.cc (right):

https://codereview.chromium.org/530313002/diff/1/runtime/vm/parser.cc#newcode...
runtime/vm/parser.cc:8595: AstNode* await_preamble = CloseBlock();
Ah yes, this has bitten me in the past as well. 

On 2014/09/03 00:10:44, Michael Lippautz wrote:
> the fix is to not use
> 
> current_block_->statements->Add(CloseBlock())
> 
> as CloseBlock() changes current_block_ and gcc/clang disagree on what to
> evaluate first (args or base ptr).
> 
> It's also more readable this way :)

[srdjan, 2014-09-03 16:12:29]

lgtm

[Michael Lippautz (Google), 2014-09-03 16:34:06]

Committed patchset #1 (id:1) manually as 39810 (presubmit successful).