Add a browser test for the views external protocol dialog.

chrome/browser/ui/views/external_protocol_dialog.cc

Index: chrome/browser/ui/views/external_protocol_dialog.cc
diff --git a/chrome/browser/ui/views/external_protocol_dialog.cc b/chrome/browser/ui/views/external_protocol_dialog.cc
index 1cfc6c81bc2e221940b17399f9486d9d55ab15a2..2c795081b6feb1c9813fb8797d426ac5dc42ccef 100644
--- a/chrome/browser/ui/views/external_protocol_dialog.cc
+++ b/chrome/browser/ui/views/external_protocol_dialog.cc
@@ -53,6 +53,10 @@ void ExternalProtocolHandler::RunExternalProtocolDialog(
 ExternalProtocolDialog::~ExternalProtocolDialog() {
 }
 
+void ExternalProtocolDialog::SetCheckBoxSelectedForTesting(bool checked) {
+  message_box_view_->SetCheckBoxSelected(checked);
+}
+
 //////////////////////////////////////////////////////////////////////////////
 // ExternalProtocolDialog, views::DialogDelegate implementation: