Implement type cast in the VM.

runtime/vm/exceptions.cc

Index: runtime/vm/exceptions.cc
===================================================================
--- runtime/vm/exceptions.cc	(revision 9048)
+++ runtime/vm/exceptions.cc	(working copy)
@@ -182,13 +182,21 @@
                                          const String& dst_type_name,
                                          const String& dst_name,
                                          const String& malformed_error) {
-  // Allocate a new instance of TypeError.
-  const Instance& type_error = Instance::Handle(NewInstance("TypeError"));
+  // Allocate a new instance of TypeError or CastException.
+  Instance& type_error = Instance::Handle();
+  Class& cls = Class::Handle();
+  if (dst_name.Equals("type cast")) {
+    type_error = NewInstance("CastException");
+    cls = type_error.clazz();
+    cls = cls.SuperClass();
+  } else {
+    type_error = NewInstance("TypeError");
+    cls = type_error.clazz();
+  }
 
   // Initialize 'url', 'line', and 'column' fields.
   DartFrameIterator iterator;
   const Script& script = Script::Handle(GetCallerScript(&iterator));
-  const Class& cls = Class::Handle(type_error.clazz());
   // Location fields are defined in AssertionError, the superclass of TypeError.
   const Class& assertion_error_class = Class::Handle(cls.SuperClass());
   SetLocationFields(type_error, assertion_error_class, script, location);