Simplify BodyBuilder's Identifier class.

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

 // Copyright (c) 2016, 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.
 
 library fasta.body_builder;
 
 import '../fasta_codes.dart'
     show FastaMessage, codeExpectedButGot, codeExpectedFunctionBody;
 
 import '../parser/parser.dart' show FormalParameterType, optional;
@@ skipping 1340 matching lines @@
     } else {
       return internalError("Unhandled: ${name.runtimeType}");
     }
   }
 
   @override
   void endLiteralSymbol(Token hashToken, int identifierCount) {
     debugEvent("LiteralSymbol");
     String value;
     if (identifierCount == 1) {
-      value = symbolPartToString(popForValue());
+      value = symbolPartToString(pop());
     } else {
       List parts = popList(identifierCount);
       value = symbolPartToString(parts.first);
       for (int i = 1; i < parts.length; i++) {
         value += ".${symbolPartToString(parts[i])}";
       }
     }
     push(new SymbolLiteral(value));
   }
 
@@ skipping 1287 matching lines @@
     if (fieldDependencies != null && readTarget is KernelField) {
       var fieldNode = _typeInferrer.getFieldNodeForReadTarget(readTarget);
       if (fieldNode != null) {
         fieldDependencies.add(fieldNode);
       }
     }
     return astFactory.staticGet(readTarget, offset);
   }
 }
 
-// TODO(ahe): Shouldn't need to be an expression.
-class Identifier extends InvalidExpression {
+class Identifier {
   final String name;
+  final int fileOffset;
 
-  Identifier(this.name, int charOffset) {
-    fileOffset = charOffset;
-  }
+  Identifier(this.name, int charOffset) : fileOffset = charOffset;
 
   Expression get initializer => null;
 
   String toString() => "identifier($name)";
 }
 
 // TODO(ahe): Shouldn't need to be an expression.
 class Operator extends InvalidExpression {
   final String name;
 
@@ skipping 439 matching lines @@
   } else if (node is PrefixBuilder) {
     return node.name;
   } else if (node is ThisAccessor) {
     return node.isSuper ? "super" : "this";
   } else if (node is FastaAccessor) {
     return node.plainNameForRead;
   } else {
     return internalError("Unhandled: ${node.runtimeType}");
   }
 }