Implement type cast in the VM.

runtime/lib/error.dart

 // Copyright (c) 2012, 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.
 // Errors are created and thrown by DartVM only.
 // Changes here should also be reflected in corelib/error.dart as well
 
 class AssertionError {
   factory AssertionError._uninstantiable() {
     throw const UnsupportedOperationException(
         "AssertionError can only be allocated by the VM");
@@ skipping 30 matching lines @@
       str = "${str}malformed type used.";
     }
     return str;
   }
   final String srcType;
   final String dstType;
   final String dstName;
   final String malformedError;
 }
 
+class CastException extends TypeError {
+  factory CastException._uninstantiable() {
+    throw const UnsupportedOperationException(
+        "CastException can only be allocated by the VM");
+  }
+  // A CastException is allocated by TypeError._throwNew() with "type cast" as
+  // dst_name.
+  String toString() {
+    String str = (malformedError != null) ? malformedError : "";
+    if ((dstName != null) && (dstName.length > 0)) {
+      str = "${str}type '$srcType' is not a subtype of "
+            "type '$dstType' in type cast.";
+    } else {
+      str = "${str}malformed type used in type cast.";
+    }
+    return str;
+  }
+}
+
 class FallThroughError {
   factory FallThroughError._uninstantiable() {
     throw const UnsupportedOperationException(
         "FallThroughError can only be allocated by the VM");
   }
   static _throwNew(int case_clause_pos) native "FallThroughError_throwNew";
   String toString() {
     return "'$url': Switch case fall-through at line $line.";
   }
   final String url;
@@ skipping 16 matching lines @@
   String toString() => "Unresolved static method: url '$url' line $line "
       "pos $column\n$failedResolutionLine\n";
 
   static _throwNew(int token_pos) native "StaticResolutionException_throwNew";
 
   final String failedResolutionLine;
   final String url;
   final int line;
   final int column;
 }