Start implementing checked mode and tools support for using it.

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 2128 matching lines @@
 
   HType get guaranteedType() => HType.BOOLEAN;
 
   accept(HVisitor visitor) => visitor.visitIs(this);
 
   toString() => "$expression is $typeExpression";
 }
 
 class HTypeConversion extends HInstruction {
   HType type;
+  final bool checked;
 
-  HTypeConversion(HType this.type, HInstruction input)
-    : super(<HInstruction>[input]);
+  HTypeConversion(HType this.type,
+                  HInstruction input,
+                  [bool this.checked = false])
+    : super(<HInstruction>[input]) {
+      sourceElement = input.sourceElement;
+  }
 
   HType get guaranteedType() => type;
 
-  void prepareGvn() {
-    assert(!hasSideEffects());
-    setUseGvn();
-  }
-
   accept(HVisitor visitor) => visitor.visitTypeConversion(this);
-  int typeCode() => 27;
-  bool typeEquals(other) => other is HTypeConversion;
-  bool dataEquals(HTypeConversion other) => type == other.type;
 }
 
 /**
  * Information about a syntactic-like structure that can be attached
  * to a [HBasicBlock].
  */
 interface HBlockInformation {
   HBasicBlock get start();
   HBasicBlock get end();
   bool accept(HBlockInformationVisitor visitor);
@@ skipping 234 matching lines @@
                        this.finallyBlock,
                        this.joinBlock);
 
   HBasicBlock get start() => body.start;
   HBasicBlock get end() =>
       finallyBlock === null ? catchBlock.end : finallyBlock.end;
 
   bool accept(HStatementInformationVisitor visitor) =>
     visitor.visitTryInfo(this);
 }