Infer only ClassElementImpl in InstanceMemberInferrer, tweaks for link.

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 ccb1e7ca5989c9a393f37c96b0ef9487e01e0daf..81ae8543ab3271d03fb252a6948ba69669cca432 100644
--- a/pkg/analyzer/lib/src/summary/link.dart
+++ b/pkg/analyzer/lib/src/summary/link.dart
@@ -388,9 +388,6 @@ abstract class ClassElementForLink extends Object
   String get name;
 
   @override
-  ResynthesizerContext get resynthesizerContext => enclosingElement;
-
-  @override
   ConstructorElementForLink get unnamedConstructor;
 
   @override
@@ -427,7 +424,8 @@ abstract class ClassElementForLink extends Object
  * linking.
  */
 class ClassElementForLink_Class extends ClassElementForLink
-    with TypeParameterizedElementMixin {
+    with TypeParameterizedElementMixin
+    implements ClassElementImpl {
   /**
    * The unlinked representation of the class in the summary.
    */
@@ -675,7 +673,8 @@ class ClassElementForLink_Class extends ClassElementForLink
  * Element representing an enum resynthesized from a summary during
  * linking.
  */
-class ClassElementForLink_Enum extends ClassElementForLink {
+class ClassElementForLink_Enum extends ClassElementForLink
+    implements EnumElementImpl {
   /**
    * The unlinked representation of the enum in the summary.
    */