Support 'on T' catch clauses and multiple clauses.

Support 'on T' catch clauses and multiple clauses.

The sequence of clauses is translated into the corresponding nested if-else
statements.  The last else is the catch-all clause (no 'on T') if there is
one or implicitly 'rethrow' otherwise.

If there is a catch-all clause (no 'on T'), then any clauses after it
are unreachable.  The language specification allows such unreachable
clauses without an error.

R=asgerf@google.com, karlklose@google.com
BUG=

Committed: https://code.google.com/p/dart/source/detail?r=45634

[Kevin Millikin (Google), 2015-05-05 10:29:12]

I inspected the JS output of most of the now-passing tests, it is correct but
there are some things to clean up.

Many of the tests that failed due to lacking support for multiple catch clauses
now fail for another reason.  Karl has a script to update the test expectations.

https://codereview.chromium.org/1125813004/diff/1/pkg/compiler/lib/src/cps_ir...
File pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart (right):

https://codereview.chromium.org/1125813004/diff/1/pkg/compiler/lib/src/cps_ir...
pkg/compiler/lib/src/cps_ir/cps_ir_builder.dart:1815: IrBuilder clauseBuilder =
catchBuilder.makeDelimitedBuilder();
I'm going to move the next seven or eight lines into a named helper, because
they're duplicated inside the loop too.

[asgerf, 2015-05-05 10:39:28]

LGTM!

[Kevin Millikin (Google), 2015-05-08 08:49:39]

Committed patchset #1 (id:1) manually as 45634 (presubmit successful).