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

chrome/browser/webshare/share_service_impl.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_WEBSHARE_SHARE_SERVICE_IMPL_H_
 #define CHROME_BROWSER_WEBSHARE_SHARE_SERVICE_IMPL_H_
 
 #include <memory>
 #include <string>
 #include <vector>
@@ skipping 39 matching lines @@
   // Returns the site engagement level of the site, |url|, with the user.
   // Virtual for testing purposes.
   virtual blink::mojom::EngagementLevel GetEngagementLevel(const GURL& url);
 
   // Shows the share picker dialog with |targets| as the list of applications
   // presented to the user. Passes the result to |callback|. If the user picks a
   // target, the result passed to |callback| is the manifest URL of the chosen
   // target, or is null if the user cancelled the share. Virtual for testing.
   virtual void ShowPickerDialog(
       const std::vector<std::pair<base::string16, GURL>>& targets,
-      const base::Callback<void(base::Optional<std::string>)>& callback);
+      chrome::WebShareTargetPickerCallback callback);
 
   // Opens a new tab and navigates to |target_url|.
   // Virtual for testing purposes.
   virtual void OpenTargetURL(const GURL& target_url);
 
   // Returns all stored Share Targets that have a high enough engagement score
   // with the user.
   std::vector<std::pair<base::string16, GURL>>
   GetTargetsWithSufficientEngagement(
       const base::DictionaryValue& share_targets);
@@ skipping 10 matching lines @@
                                   base::StringPiece title,
                                   base::StringPiece text,
                                   const GURL& share_url,
                                   std::string* url_template_filled);
 
   void OnPickerClosed(std::unique_ptr<base::DictionaryValue> share_targets,
                       const std::string& title,
                       const std::string& text,
                       const GURL& share_url,
                       const ShareCallback& callback,
-                      base::Optional<std::string> result);
+                      const base::Optional<std::string>& result);
 
   base::WeakPtrFactory<ShareServiceImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ShareServiceImpl);
 };
 
 #endif  // CHROME_BROWSER_WEBSHARE_SHARE_SERVICE_IMPL_H_