Improve async code in VM by not unnecessarily capturing parameters of async and

Improve async code in VM by not unnecessarily capturing parameters of async and
sync closures, thereby avoiding copy of parameters on entry.
Remove variable aliases in local scopes now that another mechanism detects
use-before-define cases. Keep aliases only for captured variables of outer
functions thereby speeding up scope lookups for all Dart code (not just async).
The next step will be to try to reduce the number of captured variables in
async code.

R=hausner@google.com

Committed: https://github.com/dart-lang/sdk/commit/e6225bee44fab8c5edfb7a167eecc09db23dd8c8

[regis, 2015-08-27 22:37:41]

regis@google.com changed reviewers:
+ hausner@google.com

[hausner, 2015-08-27 23:21:20]

LGTM.

This is the nicest cleanup change I've seen in a long time!

[regis, 2015-08-27 23:48:47]

Thanks!

I have made a little improvement before submitting.

[regis, 2015-08-27 23:49:11]

Committed patchset #2 (id:20001) manually as
e6225bee44fab8c5edfb7a167eecc09db23dd8c8 (presubmit successful).