Implement try/catch in the JS backend.

Implement try/catch in the JS backend.

In the CPS IR, exception handlers initially have two parameters for
the exception and the stack trace.  In JavaScript:

1. Unwrap the caught value to get the exception that was thrown and
   use the unwrapped value in place of the exception parameter.

2. Get the stack trace from the (unwrapped) exception that was thrown.

3. Remove the stack trace parameter.

BUG=
R=asgerf@google.com

Committed: https://code.google.com/p/dart/source/detail?r=45152

[Kevin Millikin (Google), 2015-04-14 12:08:06]

kmillikin@google.com changed reviewers:
+ asgerf@google.com, karlklose@google.com, sra@google.com

[Kevin Millikin (Google), 2015-04-14 12:08:07]

I'm using the Dart mutable variable analysis in the JS backend out of
expediency, but I plan to change that later.

[asgerf, 2015-04-14 12:59:17]

LGTM

https://codereview.chromium.org/1083663005/diff/1/pkg/compiler/lib/src/js_bac...
File pkg/compiler/lib/src/js_backend/codegen/unsugar.dart (right):

https://codereview.chromium.org/1083663005/diff/1/pkg/compiler/lib/src/js_bac...
pkg/compiler/lib/src/js_backend/codegen/unsugar.dart:18: ///  - rewrite [IsTrue]
in a [Branch] to do boolean conversion.
Stale doc comment.

https://codereview.chromium.org/1083663005/diff/1/pkg/compiler/lib/src/js_bac...
pkg/compiler/lib/src/js_backend/codegen/unsugar.dart:63: /// the result, and
then insert the call with this function.
The result parameter *is* passed ...

I don't see why we need the last comment, though. I think it's common enough to
tell a code generating function where to put the result.

[Kevin Millikin (Google), 2015-04-15 07:52:23]

https://codereview.chromium.org/1083663005/diff/1/pkg/compiler/lib/src/js_bac...
File pkg/compiler/lib/src/js_backend/codegen/unsugar.dart (right):

https://codereview.chromium.org/1083663005/diff/1/pkg/compiler/lib/src/js_bac...
pkg/compiler/lib/src/js_backend/codegen/unsugar.dart:18: ///  - rewrite [IsTrue]
in a [Branch] to do boolean conversion.
On 2015/04/14 12:59:17, asgerf wrote:
> Stale doc comment.

Thanks, updated.

https://codereview.chromium.org/1083663005/diff/1/pkg/compiler/lib/src/js_bac...
pkg/compiler/lib/src/js_backend/codegen/unsugar.dart:63: /// the result, and
then insert the call with this function.
On 2015/04/14 12:59:17, asgerf wrote:
> The result parameter *is* passed ...
> 
> I don't see why we need the last comment, though. I think it's common enough
to
> tell a code generating function where to put the result.

Fair enough, I'll just remove that bit of the comment.

[Kevin Millikin (Google), 2015-04-15 07:56:51]

Committed patchset #2 (id:20001) manually as 45152 (presubmit successful).