Fixes for checked mode and change buildbot script to run dart2js tests in checked mode also.

lib/compiler/implementation/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 visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
   R visitBitXor(HBitXor node);
@@ skipping 946 matching lines @@
   }
 
   HType get guaranteedType() => HType.BOOLEAN;
 
   accept(HVisitor visitor) => visitor.visitBoolify(this);
   int typeCode() => 0;
   bool typeEquals(other) => other is HBoolify;
   bool dataEquals(HInstruction other) => true;
 }
 
-class HCheck extends HInstruction {
+/**
+ * A [HCheck] instruction is an instruction that might do a dynamic
+ * check at runtime on another instruction. To have proper instruction
+ * dependencies in the graph, instructions that depend on the check
+ * being done reference the [HCheck] instruction instead of the
+ * instruction itself.
+ */
+abstract class HCheck extends HInstruction {
   HCheck(inputs) : super(inputs);
-
-  // TODO(floitsch): make class abstract instead of adding an abstract method.
-  abstract accept(HVisitor visitor);
-
   HInstruction get checkedInput() => inputs[0];
 }
 
 class HTypeGuard extends HCheck {
   final int state;
   final HType guardedType;
   bool isOn = false;
   HTypeGuard(this.guardedType, this.state, List<HInstruction> env) : super(env);
 
   void prepareGvn() {
@@ skipping 1581 matching lines @@
   HBasicBlock get start() => expression.start;
   HBasicBlock get end() {
     // We don't create a switch block if there are no cases.
     assert(!statements.isEmpty());
     return statements.last().end;
   }
 
   bool accept(HStatementInformationVisitor visitor) =>
       visitor.visitSwitchInfo(this);
 }