Implement Increment and Decrement accessible actions

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 30bde3590748457baf1dc8e274b5793815e8c0f5..f98a05ffd1f3bb5692ed1dc89dacc6ba597f828a 100644
--- a/ui/accessibility/ax_enums.idl
+++ b/ui/accessibility/ax_enums.idl
@@ -232,6 +232,9 @@
 
   // An action to be taken on an accessibility node.
   enum AXAction {
+    // Decrement a slider or range control by one step value.
+    decrement,
+
     // Do the default action for an object, typically this means "click".
     do_default,
 
@@ -239,6 +242,9 @@
     // HOVER event on it in response.
     hit_test,
 
+    // Increment a slider or range control by one step value.
+    increment,
+
     // Delete any selected text in the control's text value and
     // insert |AXActionData::value| in its place, like when typing or pasting.
     replace_selected_text,
@@ -460,7 +466,7 @@
     // within the object's bounds, the second offset is the right coordinate
     // of the second character, and so on.
     character_offsets,
-    
+
     // Used for caching. Do not read directly. Use
     // |AXNode::GetOrComputeLineStartOffsets|
     // For all text fields and content editable roots: A list of the start