Flatten the AST for try/catch.

Flatten the AST for try/catch.

Flatten a pair of blocks where the outer one is solely used to hold
the bindings of the parameters and to contain the inner one.

R=fschneider@google.com

Committed: https://code.google.com/p/dart/source/detail?r=29889

[Florian Schneider, 2013-11-05 10:05:30]

lgtm

https://codereview.chromium.org/59523002/diff/1/runtime/vm/parser.cc
File runtime/vm/parser.cc (right):

https://codereview.chromium.org/59523002/diff/1/runtime/vm/parser.cc#newcode1100
runtime/vm/parser.cc:1100: OpenBlock();  // Start catch clause.
The same should be done here for try-catch generated here.

[Kevin Millikin (Google), 2013-11-05 11:21:04]

Committed patchset #1 manually as r29889 (presubmit successful).

[hausner, 2013-11-05 18:53:41]

This change broke the compiler. The reason there were two nested blocks is
because the exception and stack trace variables are declared in an invisible 
block that encloses the visible block of the catch clause. This allows users to
shadow the exception and stack trace variables. Your change puts the exception
and stack trace variables inside the catch block, making it an error if another
variable with the same name is defined.

dart2js allows the shadowing, so you also introduced an incompatibility.

This said, there was is a bug in the way the two nested blocks were used prior
to your change.

I'll revert this change and fix the previous bug.