All strong mode cleaning of dart2js.

pkg/compiler/lib/src/parser/partial_elements.dart

Index: pkg/compiler/lib/src/parser/partial_elements.dart
diff --git a/pkg/compiler/lib/src/parser/partial_elements.dart b/pkg/compiler/lib/src/parser/partial_elements.dart
index 899f686a3a0239bb9e1285974d2294798440ef54..f0cc9956d4a932a4842ea6be1e4ab7095b06684e 100644
--- a/pkg/compiler/lib/src/parser/partial_elements.dart
+++ b/pkg/compiler/lib/src/parser/partial_elements.dart
@@ -139,6 +139,7 @@ abstract class PartialFunctionElement
   PartialFunctionElement copyWithEnclosing(Element enclosing);
 }
 
+// ignore: STRONG_MODE_INVALID_METHOD_OVERRIDE_FROM_BASE
 class PartialMethodElement extends MethodElementX
     with PartialElement, PartialFunctionMixin
     implements PartialFunctionElement {
@@ -161,6 +162,7 @@ class PartialMethodElement extends MethodElementX
   }
 }
 
+// ignore: STRONG_MODE_INVALID_METHOD_OVERRIDE_FROM_BASE
 class PartialGetterElement extends GetterElementX
     with PartialElement, PartialFunctionMixin
     implements GetterElement, PartialFunctionElement {
@@ -186,6 +188,7 @@ class PartialGetterElement extends GetterElementX
   }
 }
 
+// ignore: STRONG_MODE_INVALID_METHOD_OVERRIDE_FROM_BASE
 class PartialSetterElement extends SetterElementX
     with PartialElement, PartialFunctionMixin
     implements SetterElement, PartialFunctionElement {