Make ExecutableElementImpl implement TypeParameterizedElementMixin.

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 970087cacf8154c8c89c6e5b7e6a35767cd43119..e14e994b4a261feed7bec075c015d05c1e8467a8 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -1611,6 +1611,10 @@ class ConstructorElementImpl extends ExecutableElementImpl
   @override
   ClassElement get enclosingElement => super.enclosingElement as ClassElement;
 
+  @override
+  TypeParameterizedElementMixin get enclosingTypeParameterContext =>
+      super.enclosingElement as ClassElementImpl;
+
   /**
    * Set whether this constructor represents a factory method.
    */
@@ -2692,6 +2696,7 @@ class ElementLocationImpl implements ElementLocation {
  * A base class for concrete implementations of an [ExecutableElement].
  */
 abstract class ExecutableElementImpl extends ElementImpl
+    with TypeParameterizedElementMixin
     implements ExecutableElement {
   /**
    * The unlinked representation of the executable in the summary.
@@ -2979,6 +2984,10 @@ abstract class ExecutableElementImpl extends ElementImpl
   }
 
   @override
+  List<UnlinkedTypeParam> get unlinkedTypeParams =>
+      serializedExecutable.typeParameters;
+
+  @override
   void appendTo(StringBuffer buffer) {
     if (this.kind != ElementKind.GETTER) {
       int typeParameterCount = _typeParameters.length;
@@ -3251,6 +3260,15 @@ class FunctionElementImpl extends ExecutableElementImpl
   }
 
   @override
+  TypeParameterizedElementMixin get enclosingTypeParameterContext {
+    Element enclosingElement = this.enclosingElement;
+    if (enclosingElement is TypeParameterizedElementMixin) {
+      return enclosingElement;
+    }
+    return null;
+  }
+
+  @override
   String get identifier {
     String identifier = super.identifier;
     if (!isStatic) {
@@ -4548,6 +4566,10 @@ class MethodElementImpl extends ExecutableElementImpl implements MethodElement {
   ClassElement get enclosingElement => super.enclosingElement as ClassElement;
 
   @override
+  TypeParameterizedElementMixin get enclosingTypeParameterContext =>
+      super.enclosingElement as ClassElementImpl;
+
+  @override
   bool get isOperator {
     String name = displayName;
     if (name.isEmpty) {
@@ -4985,6 +5007,9 @@ class MultiplyInheritedPropertyAccessorElementImpl
   }
 
   @override
+  TypeParameterizedElementMixin get enclosingTypeParameterContext => null;
+
+  @override
   List<ExecutableElement> get inheritedElements => _elements;
 
   void set inheritedElements(List<ExecutableElement> elements) {
@@ -5562,6 +5587,15 @@ class PropertyAccessorElementImpl extends ExecutableElementImpl
     return super.displayName;
   }
 
+  @override
+  TypeParameterizedElementMixin get enclosingTypeParameterContext {
+    Element enclosingElement = this.enclosingElement;
+    if (enclosingElement is TypeParameterizedElementMixin) {
+      return enclosingElement;
+    }
+    return null;
+  }
+
   /**
    * Set whether this accessor is a getter.
    */