Mark refactoring support for plugins as experimental

pkg/analyzer_plugin/tool/spec/plugin_spec.html

Index: pkg/analyzer_plugin/tool/spec/plugin_spec.html
diff --git a/pkg/analyzer_plugin/tool/spec/plugin_spec.html b/pkg/analyzer_plugin/tool/spec/plugin_spec.html
index fc90a2c1735b2bee23cd473da8fe3ecfe84b7257..dc3fe7652e2b92c8a5ca9f24446857feda863f64 100644
--- a/pkg/analyzer_plugin/tool/spec/plugin_spec.html
+++ b/pkg/analyzer_plugin/tool/spec/plugin_spec.html
@@ -643,7 +643,7 @@
       </field>
     </result>
   </request>
-  <request method="getAvailableRefactorings">
+  <request method="getAvailableRefactorings" experimental="true">
     <p>
       Used to request a list of the kinds of refactorings that are valid for the
       given selection in the given file.
@@ -715,7 +715,7 @@
       </field>
     </result>
   </request>
-  <request method="getRefactoring">
+  <request method="getRefactoring" experimental="true">
     <p>
       Used to request the changes required to perform a refactoring.
     </p>
@@ -921,14 +921,14 @@
       </field>
     </object>
   </type>
-  <type name="RefactoringFeedback">
+  <type name="RefactoringFeedback" experimental="true">
     <p>
       An abstract superclass of all refactoring feedbacks.
     </p>
     <object>
     </object>
   </type>
-  <type name="RefactoringOptions">
+  <type name="RefactoringOptions" experimental="true">
     <p>
       An abstract superclass of all refactoring options.
     </p>