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..dc38cef3fa1da6f398bf5745c35c8d0b3bdb21c1 100644
--- a/ui/accessibility/platform/ax_platform_node_delegate.h
+++ b/ui/accessibility/platform/ax_platform_node_delegate.h
@@ -85,9 +85,13 @@ class AX_EXPORT AXPlatformNodeDelegate {
   virtual void DoDefaultAction() = 0;
 
   // Change the value of a control, such as the text content of a text field.
-  virtual bool SetStringValue(const base::string16& new_value) = 0;
+  // Set |clear_first| to true to clear the existing value first, false to
+  // replace the currently selected text.
+  virtual bool SetStringValue(const base::string16& new_value,
+                              bool clear_first) = 0;
 
-  // Whether the string value is settable.
+  // Whether SetStringValue() is callable, i.e. if the string value is read only
+  // and if the callback exists.
   virtual bool CanSetStringValue() = 0;
 };