Fully support try/catch.

frog/leg/ssa/nodes.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
@@ skipping 1617 matching lines @@
   accept(HVisitor visitor) => visitor.visitExit(this);
 }
 
 class HGoto extends HControlFlow {
   HGoto() : super(const <HInstruction>[]);
   toString() => 'goto';
   accept(HVisitor visitor) => visitor.visitGoto(this);
 }
 
 class HTry extends HControlFlow {
+  HParameterValue exception;
   HBasicBlock finallyBlock;
   HTry() : super(const <HInstruction>[]);
   toString() => 'try';
   accept(HVisitor visitor) => visitor.visitTry(this);
 }
 
 class HIf extends HConditionalBranch {
   bool hasElse;
   HIf(HInstruction condition, this.hasElse) : super(<HInstruction>[condition]);
   toString() => 'if';
@@ skipping 482 matching lines @@
 
   HInstruction get expression() => inputs[0];
 
   HType computeType() => HType.BOOLEAN;
   bool hasExpectedType() => true;
 
   accept(HVisitor visitor) => visitor.visitIs(this);
 
   toString() => "$expression is $typeExpression";
 }