Fix more strong mode errors in analyzer

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

Index: pkg/analyzer/lib/src/dart/element/handle.dart
diff --git a/pkg/analyzer/lib/src/dart/element/handle.dart b/pkg/analyzer/lib/src/dart/element/handle.dart
index 8cde8d0c43e985aa1bb81bfde4fd3813540ad8df..8e9fcffad448e673e5c9cad90fd4bd65bc872f24 100644
--- a/pkg/analyzer/lib/src/dart/element/handle.dart
+++ b/pkg/analyzer/lib/src/dart/element/handle.dart
@@ -95,6 +95,9 @@ class ClassElementHandle extends ElementHandle implements ClassElement {
   ConstructorElement get unnamedConstructor => actualElement.unnamedConstructor;
 
   @override
+  NamedCompilationUnitMember computeNode() => super.computeNode();
+
+  @override
   FieldElement getField(String fieldName) => actualElement.getField(fieldName);
 
   @override
@@ -895,6 +898,9 @@ class ParameterElementHandle extends VariableElementHandle
 
   @override
   SourceRange get visibleRange => actualElement.visibleRange;
+
+  @override
+  FormalParameter computeNode() => super.computeNode();
 }
 
 /**
@@ -1013,6 +1019,9 @@ class TopLevelVariableElementHandle extends PropertyInducingElementHandle
 
   @override
   ElementKind get kind => ElementKind.TOP_LEVEL_VARIABLE;
+
+  @override
+  VariableDeclaration computeNode() => super.computeNode();
 }
 
 /**
@@ -1075,10 +1084,12 @@ abstract class VariableElementHandle extends ElementHandle
   @override
   bool get isFinal => actualElement.isFinal;
 
+  @deprecated
   @override
   bool get isPotentiallyMutatedInClosure =>
       actualElement.isPotentiallyMutatedInClosure;
 
+  @deprecated
   @override
   bool get isPotentiallyMutatedInScope =>
       actualElement.isPotentiallyMutatedInScope;