Revert "Remove Registry from registerMetadataConstant" and "Serialize metadata"

pkg/compiler/lib/src/js_backend/constant_emitter.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.
 
 part of js_backend;
 
 typedef jsAst.Expression _ConstantReferenceGenerator(ConstantValue constant);
 
 typedef jsAst.Expression _ConstantListGenerator(jsAst.Expression array);
 
@@ skipping 46 matching lines @@
     reporter.internalError(NO_LOCATION_SPANNABLE,
         "The function constant does not need specific JS code.");
     return null;
   }
 
   @override
   jsAst.Expression visitNull(NullConstantValue constant, [_]) {
     return new jsAst.LiteralNull();
   }
 
-  @override
-  jsAst.Expression visitNonConstant(NonConstantValue constant, [_]) {
-    return new jsAst.LiteralNull();
-  }
-
   static final _exponentialRE = new RegExp('^'
       '\([-+]?\)' // 1: sign
       '\([0-9]+\)' // 2: leading digit(s)
       '\(\.\([0-9]*\)\)?' // 4: fraction digits
       'e\([-+]?[0-9]+\)' // 5: exponent with sign
       r'$');
 
   /// Reduces the size of exponential representations when minification is
   /// enabled.
   ///
@@ skipping 239 matching lines @@
           [value, argumentList]);
     }
     return value;
   }
 
   @override
   jsAst.Expression visitDeferred(DeferredConstantValue constant, [_]) {
     return constantReferenceGenerator(constant.referenced);
   }
 }