webshare: Small refactor of WebShare (OnceCallback, const&, and alias)

chrome/browser/ui/views/webshare/webshare_target_picker_view.cc

Index: chrome/browser/ui/views/webshare/webshare_target_picker_view.cc
diff --git a/chrome/browser/ui/views/webshare/webshare_target_picker_view.cc b/chrome/browser/ui/views/webshare/webshare_target_picker_view.cc
index 97d6dea26f270f119c636f89a934de4ecc53d2d6..e5675a3443ea659fe4ddeb48de19079d100e3c35 100644
--- a/chrome/browser/ui/views/webshare/webshare_target_picker_view.cc
+++ b/chrome/browser/ui/views/webshare/webshare_target_picker_view.cc
@@ -66,7 +66,7 @@ namespace chrome {
 void ShowWebShareTargetPickerDialog(
     gfx::NativeWindow parent_window,
     const std::vector<std::pair<base::string16, GURL>>& targets,
-    const base::Callback<void(base::Optional<std::string>)>& callback) {
+    const chrome::WebShareTargetPickerCallback& callback) {
   constrained_window::CreateBrowserModalDialogViews(
       new WebShareTargetPickerView(targets, callback), parent_window)
       ->Show();
@@ -76,7 +76,7 @@ void ShowWebShareTargetPickerDialog(
 
 WebShareTargetPickerView::WebShareTargetPickerView(
     const std::vector<std::pair<base::string16, GURL>>& targets,
-    const base::Callback<void(base::Optional<std::string>)>& close_callback)
+    const chrome::WebShareTargetPickerCallback& close_callback)
     : targets_(targets),
       table_model_(base::MakeUnique<TargetPickerTableModel>(&targets_)),
       close_callback_(close_callback) {