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

ui/views/controls/textfield/textfield.cc

Index: ui/views/controls/textfield/textfield.cc
diff --git a/ui/views/controls/textfield/textfield.cc b/ui/views/controls/textfield/textfield.cc
index 4163c40a3742095f01fec3da7cf14d44db94aae4..0b9b5b7efff15baccac6d05d8472f60bf9c979b2 100644
--- a/ui/views/controls/textfield/textfield.cc
+++ b/ui/views/controls/textfield/textfield.cc
@@ -1808,11 +1808,15 @@ void Textfield::ExecuteTextEditCommand(ui::TextEditCommand command) {
 ////////////////////////////////////////////////////////////////////////////////
 // Textfield, private:
 
-void Textfield::AccessibilitySetValue(const base::string16& new_value) {
-  if (!read_only()) {
+void Textfield::AccessibilitySetValue(const base::string16& new_value,
+                                      bool clear_first) {
+  if (read_only())
+    return;
+  if (!clear_first)
+    InsertOrReplaceText(new_value);
+  else
     SetText(new_value);
-    ClearSelection();
-  }
+  ClearSelection();
 }
 
 void Textfield::UpdateBackgroundColor() {