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

ui/accessibility/ax_view_state.h

Index: ui/accessibility/ax_view_state.h
diff --git a/ui/accessibility/ax_view_state.h b/ui/accessibility/ax_view_state.h
index a20a65d6e7d41190cf9562522913e6b535b8c0e7..9784fe7d7075fb18f7a7014a9c17ed42b3197622 100644
--- a/ui/accessibility/ax_view_state.h
+++ b/ui/accessibility/ax_view_state.h
@@ -75,12 +75,14 @@ struct AX_EXPORT AXViewState {
   // set the string value of this view. This only applies to roles where
   // setting the value makes sense, like a text box. Not often used by
   // screen readers, but often used by automation software to script
-  // things like logging into portals or filling forms.
+  // things like logging into portals or filling forms. Set the second argument
+  // to true to clear the existing value first, false to replace the currently
+  // selected text.
   //
   // This callback is only valid for the lifetime of the view, and should
   // be a safe no-op if the view is deleted. Typically, accessible views
   // should use a WeakPtr when binding the callback.
-  base::Callback<void(const base::string16&)> set_value_callback;
+  base::Callback<void(const base::string16&, bool)> set_value_callback;
 
  private:
   uint32_t state_;