Start pulling apart ClassElementImpl and EnumElementImpl.

pkg/analyzer/lib/src/generated/incremental_resolver.dart

Index: pkg/analyzer/lib/src/generated/incremental_resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/incremental_resolver.dart b/pkg/analyzer/lib/src/generated/incremental_resolver.dart
index fe67af5aa7f0f803f6e178ea7ba49bdee2bc5d92..b23d188b589af0cc66df8b9099a507e318a5be52 100644
--- a/pkg/analyzer/lib/src/generated/incremental_resolver.dart
+++ b/pkg/analyzer/lib/src/generated/incremental_resolver.dart
@@ -74,7 +74,13 @@ class DeclarationMatcher extends RecursiveAstVisitor {
    * The class containing the AST nodes being visited, or `null` if we are not
    * in the scope of a class.
    */
-  AbstractClassElementImpl _enclosingClass;
+  ClassElementImpl _enclosingClass;
+
+  /**
+   * The enum containing the AST nodes being visited, or `null` if we are not
+   * in the scope of an enum.
+   */
+  EnumElementImpl _enclosingEnum;
 
   /**
    * The parameter containing the AST nodes being visited, or `null` if we are not in the
@@ -214,7 +220,7 @@ class DeclarationMatcher extends RecursiveAstVisitor {
   @override
   visitEnumConstantDeclaration(EnumConstantDeclaration node) {
     String name = node.name.name;
-    FieldElement element = _findElement(_enclosingClass.fields, name);
+    FieldElement element = _findElement(_enclosingEnum.fields, name);
     _processElement(element);
   }
 
@@ -222,7 +228,7 @@ class DeclarationMatcher extends RecursiveAstVisitor {
   visitEnumDeclaration(EnumDeclaration node) {
     String name = node.name.name;
     ClassElement element = _findElement(_enclosingUnit.enums, name);
-    _enclosingClass = element;
+    _enclosingEnum = element;
     _processElement(element);
     _assertTrue(element.isEnum);
     super.visitEnumDeclaration(node);