Expose remaining 'errors' in an unified dart:core.

lib/compiler/implementation/lib/mock.dart

Index: lib/compiler/implementation/lib/mock.dart
diff --git a/lib/compiler/implementation/lib/mock.dart b/lib/compiler/implementation/lib/mock.dart
index 16fc2c05970ab1c90bfdb616a2aae35eb230fb52..159c03847eb83dde95c7fd8514bf2af6eaebd51c 100644
--- a/lib/compiler/implementation/lib/mock.dart
+++ b/lib/compiler/implementation/lib/mock.dart
@@ -6,20 +6,20 @@
 
 // TODO(ahe): Remove this file.
 
-class TypeError extends AssertionError {
+class TypeErrorImplementation implements TypeError {

[Mads Ager (google), 2012/08/28 16:01:46]

How about putting these in errors.dart. That will match the
corelib/src/errors.dart file.

   final String msg;
-  const TypeError(String this.msg);
+  const TypeErrorImplementation(String this.msg);
   String toString() => msg;
 }
 
 /** Thrown by the 'as' operator if the cast isn't valid. */
-class CastException implements TypeError {
+class CastExceptionImplementation implements CastException {
   // TODO(lrn): Change actualType and expectedType to "Type" when reified
   // types are available.
   final Object actualType;
   final Object expectedType;
 
-  CastException(this.actualType, this.expectedType);
+  CastExceptionImplementation(this.actualType, this.expectedType);
 
   String toString() {
     return "CastException: Casting value of type $actualType to"