MacViews a11y: Allow accessibility clients to set the AXValue on some controls.

ui/views/accessibility/native_view_accessibility.cc

Index: ui/views/accessibility/native_view_accessibility.cc
diff --git a/ui/views/accessibility/native_view_accessibility.cc b/ui/views/accessibility/native_view_accessibility.cc
index c10e55cc3ac51e5c358cbc316bf3af411bed9d00..9c753793a15fb56e77da30903ebc39a328cdf28f 100644
--- a/ui/views/accessibility/native_view_accessibility.cc
+++ b/ui/views/accessibility/native_view_accessibility.cc
@@ -206,15 +206,22 @@ void NativeViewAccessibility::DoDefaultAction() {
 
 bool NativeViewAccessibility::SetStringValue(const base::string16& new_value) {
   // Return an error if the view can't set the value.
-  ui::AXViewState state;
-  view_->GetAccessibleState(&state);
-  if (state.set_value_callback.is_null())
+  if (!CanSetStringValue())
     return false;
 
+  ui::AXViewState state;
+  view_->GetAccessibleState(&state);
   state.set_value_callback.Run(new_value);
   return true;
 }
 
+bool NativeViewAccessibility::CanSetStringValue() {
+  ui::AXViewState state;
+  view_->GetAccessibleState(&state);
+  return !ui::AXViewState::IsFlagSet(GetData().state, ui::AX_STATE_READ_ONLY) &&
+         !state.set_value_callback.is_null();
+}
+
 void NativeViewAccessibility::OnWidgetDestroying(Widget* widget) {
   if (parent_widget_ == widget) {
     parent_widget_->RemoveObserver(this);