Change assert implementation to not depend on a top-level function called 'assert'.

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 01303d8ad18110ed8c5cd513462f0e23734acfa3..ef49c989286310f620930dea49efb8f315a74753 100644
--- a/lib/compiler/implementation/lib/mock.dart
+++ b/lib/compiler/implementation/lib/mock.dart
@@ -6,21 +6,6 @@
 
 // TODO(ahe): Remove this file.
 
-// TODO(ahe): VM specfic exception?
-class InternalError {
-  const InternalError(this._msg);
-  String toString() => "InternalError: '${_msg}'";
-  final String _msg;
-}
-
-// TODO(ahe): VM specfic exception?
-class StaticResolutionException implements Exception {}
-
-void assert(condition) {
-  if (condition is Function) condition = condition();
-  if (!condition) throw new AssertionError();
-}
-
 // TODO(ahe): Not sure ByteArray belongs in the core library.
 interface Uint8List extends List default _InternalByteArray {
   Uint8List(int length);