Fix crash while inferencing instance field type.

pkg/analyzer/lib/src/summary/link.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.
 
 /**
  * This library is capable of producing linked summaries from unlinked
  * ones (or prelinked ones).  It functions by building a miniature
  * element model to represent the contents of the summaries, and then
  * scanning the element model to gather linked information and adding
  * it to the summary data structures.
@@ skipping 2944 matching lines @@
 
   @override
   List<FunctionElementForLink_Local_NonSynthetic> get functions =>
       _functions ??= _variable.unlinkedVariable.initializer.localFunctions
           .map((UnlinkedExecutable ex) =>
               new FunctionElementForLink_Local_NonSynthetic(
                   _variable.compilationUnit, this, ex))
           .toList();
 
   @override
+  String get identifier => '';
+
+  @override
   DartType get returnType {
     // If this is a variable whose type needs inferring, infer it.
     if (_variable.hasImplicitType) {
       return _variable.inferredType;
     } else {
       // There's no reason linking should need to access the type of
       // this FunctionElement, since the variable doesn't need its
       // type inferred.
       assert(false);
       // But for robustness, return the dynamic type.
@@ skipping 103 matching lines @@
 
   @override
   List<FunctionElementForLink_Local_NonSynthetic> get functions =>
       _functions ??= _unlinkedExecutable.localFunctions
           .map((UnlinkedExecutable ex) =>
               new FunctionElementForLink_Local_NonSynthetic(
                   compilationUnit, this, ex))
           .toList();
 
   @override
+  String get identifier {
+    String identifier = _unlinkedExecutable.name;
+    Element enclosing = this.enclosingElement;
+    if (enclosing is ExecutableElement) {
+      int id =
+          ElementImpl.findElementIndexUsingIdentical(enclosing.functions, this);
+      identifier += "@$id";
+    }
+    return identifier;
+  }
+
+  @override
   bool get _hasTypeBeenInferred => _inferredReturnType != null;
 
   @override
   DartType buildType(
       DartType getTypeArgument(int i), List<int> implicitFunctionTypeIndices) {
     assert(implicitFunctionTypeIndices.isEmpty);
     return type;
   }
 
   @override
@@ skipping 1876 matching lines @@
     }
   }
 
   @override
   PropertyAccessorElementForLink_Variable get getter =>
       _getter ??= new PropertyAccessorElementForLink_Variable(this, false);
 
   @override
   bool get hasImplicitType => unlinkedVariable.type == null;
 
+  @override
+  String get identifier => unlinkedVariable.name;
+
   /**
    * Return the inferred type of the variable element.  Should only be called if
    * no type was explicitly declared.
    */
   DartType get inferredType {
     // We should only try to infer a type when none is explicitly declared.
     assert(unlinkedVariable.type == null);
     if (_inferredType == null) {
       if (_typeInferenceNode != null) {
         assert(Linker._initializerTypeInferenceCycle == null);
@@ skipping 67 matching lines @@
    * there are no type parameters in scope.
    */
   TypeParameterizedElementMixin get _typeParameterContext;
 
   @override
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 
   @override
   String toString() => '$enclosingElement.$name';
 }