Fix crash while inferencing instance field type.

pkg/analyzer/lib/src/summary/link.dart

Index: pkg/analyzer/lib/src/summary/link.dart
diff --git a/pkg/analyzer/lib/src/summary/link.dart b/pkg/analyzer/lib/src/summary/link.dart
index 87828c393b44993dd6d8f2e77ba6b275536bea97..d24569a3dfe2b5d9943ef2b9547b31765ae72360 100644
--- a/pkg/analyzer/lib/src/summary/link.dart
+++ b/pkg/analyzer/lib/src/summary/link.dart
@@ -2962,6 +2962,9 @@ class FunctionElementForLink_Initializer extends Object
           .toList();
 
   @override
+  String get identifier => '';
+
+  @override
   DartType get returnType {
     // If this is a variable whose type needs inferring, infer it.
     if (_variable.hasImplicitType) {
@@ -3085,6 +3088,18 @@ class FunctionElementForLink_Local_NonSynthetic extends ExecutableElementForLink
           .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
@@ -4981,6 +4996,9 @@ abstract class VariableElementForLink
   @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.