Check if the method / accessor being inlined is synthetic.

pkg/analysis_server/lib/src/services/refactoring/inline_method.dart

Index: pkg/analysis_server/lib/src/services/refactoring/inline_method.dart
diff --git a/pkg/analysis_server/lib/src/services/refactoring/inline_method.dart b/pkg/analysis_server/lib/src/services/refactoring/inline_method.dart
index c55117efd840841919611315303aab7ddab93165..af2384946703e7fc57c2cc6c5f9e201a1fc79b4b 100644
--- a/pkg/analysis_server/lib/src/services/refactoring/inline_method.dart
+++ b/pkg/analysis_server/lib/src/services/refactoring/inline_method.dart
@@ -343,6 +343,9 @@ class InlineMethodRefactoringImpl extends RefactoringImpl implements
     if (element is! ExecutableElement) {
       return fatalStatus;
     }
+    if (element.isSynthetic) {
+      return fatalStatus;
+    }
     _methodElement = element as ExecutableElement;
     _isAccessor = element is PropertyAccessorElement;
     _methodUnit = element.unit;