Add custom action support

ui/accessibility/ax_enums.idl

Index: ui/accessibility/ax_enums.idl
diff --git a/ui/accessibility/ax_enums.idl b/ui/accessibility/ax_enums.idl
index 88751f8b8ccffbe93afa958f5f0749b20460fb96..d5689711bd8243f4f80d64f797e3de0efe24167a 100644
--- a/ui/accessibility/ax_enums.idl
+++ b/ui/accessibility/ax_enums.idl
@@ -247,6 +247,8 @@
   enum AXAction {
     blur,
 
+    custom_action,
+
     // Decrement a slider or range control by one step value.
     decrement,
 
@@ -531,7 +533,13 @@
     // For inline text. These int lists must be the same size; they represent
     // the start and end character offset of each word within this text.
     word_starts,
-    word_ends
+    word_ends,
+
+    custom_action_ids

[dmazzoni, 2017/06/06 03:06:00]

Add a comment for this. You could mention that they're currently only used
on Android and give a good example of a custom action there.

[yawano, 2017/06/08 09:25:29]

Done.

+  };
+
+  [cpp_enum_prefix_override="ax_attr"] enum AXStringListAttribute {
+    custom_action_descriptions
   };
 
   enum AXMarkerType {