anchor.diff:      throw UnsupportedError('compilation of an assert block');
     }
   
  +  // Replace a string `uri` literal with a cached top-level variable containing
  +  // the value to reduce overall code size.
  +  js_ast.Identifier _cacheUri(String uri) {
  +    var id = _uriMap[uri];
  +    if (id == null) {
  +      var name = 'L${_uriMap.length}';
  +      id = js_ast.TemporaryId(name);
  +      _uriMap[uri] = id;
  +    }
  +    return id;
  +  }
  +
     @override
     js_ast.Statement visitAssertStatement(AssertStatement node) {
       if (!_options.enableAsserts) return js_ast.EmptyStatement();
  
positive.code: 
    /// Maps Kernel constants to their JS aliases.
    final constAliasCache = HashMap<Constant, js_ast.Expression>();
  
    final Class _jsArrayClass;
    final Class _privateSymbolClass;
  
negative.code:       moduleItems.insert(_constTableInsertionIndex, constTableBody);
        _constLazyAccessors.clear();
      }
  
      // Add assert locations
      _uriMap.forEach((location, id) {
        moduleItems
            .add(js.statement('var # = #;', [id, js.escapedString(location)]));
      });
  
      moduleItems.addAll(afterClassDefItems);
      afterClassDefItems.clear();
  