MacViews/a11y: Allow accessibility clients to update the selected text.

ui/accessibility/platform/ax_platform_node_delegate.h

Index: ui/accessibility/platform/ax_platform_node_delegate.h
diff --git a/ui/accessibility/platform/ax_platform_node_delegate.h b/ui/accessibility/platform/ax_platform_node_delegate.h
index 1e27f3f00a09f5d3754b07db46ada6405b934882..21ac368f6b791bfaeddb106bdbe98e9b228deebc 100644
--- a/ui/accessibility/platform/ax_platform_node_delegate.h
+++ b/ui/accessibility/platform/ax_platform_node_delegate.h
@@ -86,8 +86,10 @@ class AX_EXPORT AXPlatformNodeDelegate {
 
   // Change the value of a control, such as the text content of a text field.
   virtual bool SetStringValue(const base::string16& new_value) = 0;
-
-  // Whether the string value is settable.
+  // Replace a control's selected text with new text.
+  virtual bool ReplaceSelectedText(const base::string16& new_value) = 0;
+  // Whether SetStringValue() and ReplaceSelectedText() are callable, i.e. if
+  // the string value is read only and if the callback exists.
   virtual bool CanSetStringValue() = 0;
 };