don't run dart gen on JS patch code

test/dart_codegen/expect/core/errors.dart

Index: test/dart_codegen/expect/core/errors.dart
diff --git a/test/dart_codegen/expect/core/errors.dart b/test/dart_codegen/expect/core/errors.dart
index fc92d252c17f53b03547326a2817a21b4fe3051e..d812b260e05154e63b2e90bac5b51b609e0fca3b 100644
--- a/test/dart_codegen/expect/core/errors.dart
+++ b/test/dart_codegen/expect/core/errors.dart
@@ -11,20 +11,9 @@ class Error {
     }
     return _objectToString(object);
   }
-  static String _stringToSafeString(String string) {
-    return ((__x14) => DDC$RT.cast(__x14, dynamic, String, "CastGeneral",
-        """line 89, column 12 of dart:core/errors.dart: """, __x14 is String,
-        true))(jsonEncodeNative(string));
-  }
-  static String _objectToString(Object object) {
-    return ((__x15) => DDC$RT.cast(__x15, dynamic, String, "CastGeneral",
-        """line 93, column 12 of dart:core/errors.dart: """, __x15 is String,
-        true))(Primitives.objectToString(object));
-  }
-  StackTrace get stackTrace => ((__x16) => DDC$RT.cast(__x16, dynamic,
-      StackTrace, "CastGeneral",
-      """line 96, column 32 of dart:core/errors.dart: """, __x16 is StackTrace,
-      true))(Primitives.extractStackTrace(this));
+  external static String _stringToSafeString(String string);
+  external static String _objectToString(Object object);
+  external StackTrace get stackTrace;
 }
 class AssertionError extends Error {}
 class TypeError extends AssertionError {}
@@ -91,7 +80,7 @@ class RangeError extends ArgumentError {
   static void checkValidIndex(int index, var indexable,
       [String name, int length, String message]) {
     if (length == null) length = DDC$RT.cast(indexable.length, dynamic, int,
-        "CastGeneral", """line 285, column 34 of dart:core/errors.dart: """,
+        "CastGeneral", """line 281, column 34 of dart:core/errors.dart: """,
         indexable.length is int, true);
     if (index < 0 || index >= length) {
       if (name == null) name = "index";
@@ -175,43 +164,7 @@ class NoSuchMethodError extends Error {
         _arguments = positionalArguments,
         _namedArguments = namedArguments,
         _existingArgumentNames = existingArgumentNames;
-  String toString() {
-    StringBuffer sb = new StringBuffer();
-    int i = 0;
-    if (_arguments != null) {
-      for (; i < _arguments.length; i++) {
-        if (i > 0) {
-          sb.write(", ");
-        }
-        sb.write(Error.safeToString(_arguments[i]));
-      }
-    }
-    if (_namedArguments != null) {
-      _namedArguments.forEach((Symbol key, var value) {
-        if (i > 0) {
-          sb.write(", ");
-        }
-        sb.write(_symbolToString(key));
-        sb.write(": ");
-        sb.write(Error.safeToString(value));
-        i++;
-      });
-    }
-    if (_existingArgumentNames == null) {
-      return "NoSuchMethodError : method not found: '$_memberName'\n" "Receiver: ${Error.safeToString(_receiver)}\n" "Arguments: [$sb]";
-    } else {
-      String actualParameters = sb.toString();
-      sb = new StringBuffer();
-      for (int i = 0; i < _existingArgumentNames.length; i++) {
-        if (i > 0) {
-          sb.write(", ");
-        }
-        sb.write(_existingArgumentNames[i]);
-      }
-      String formalParameters = sb.toString();
-      return "NoSuchMethodError: incorrect number of arguments passed to " "method named '$_memberName'\n" "Receiver: ${Error.safeToString(_receiver)}\n" "Tried calling: $_memberName($actualParameters)\n" "Found: $_memberName($formalParameters)";
-    }
-  }
+  external String toString();
 }
 class UnsupportedError extends Error {
   final String message;