Refactor ClipboardRecentContent singleton creation.

components/open_from_clipboard/clipboard_recent_content.h

 // Copyright 2015 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 COMPONENTS_OPEN_FROM_CLIPBOARD_CLIPBOARD_RECENT_CONTENT_H_
 #define COMPONENTS_OPEN_FROM_CLIPBOARD_CLIPBOARD_RECENT_CONTENT_H_
 
 #include <string>
 
 #include "base/macros.h"
 #include "base/time/time.h"
 
 class GURL;
 
 // Helper class returning an URL if the content of the clipboard can be turned
 // into an URL, and if it estimates that the content of the clipboard is not too
 // old.
 class ClipboardRecentContent {
  public:
-  // Returns an instance of the ClipboardContent singleton.
+  ClipboardRecentContent();
+  virtual ~ClipboardRecentContent();
+
+  // Returns the global instance of the ClipboardRecentContent singleton. This
+  // method does *not* create the singleton, and an instance must have been set
+  // via a call to SetInstance() before.
   static ClipboardRecentContent* GetInstance();
 
+  // Sets the global instance of ClipboardRecentContent singleton.
+  static void SetInstance(ClipboardRecentContent* instance);
+
   // Returns true if the clipboard contains a recent URL that has not been
   // supressed, and copies it in |url|. Otherwise, returns false. |url| must not
   // be null.
   virtual bool GetRecentURLFromClipboard(GURL* url) const = 0;
 
   // Returns how old the content of the clipboard is.
   virtual base::TimeDelta GetClipboardContentAge() const = 0;
 
   // Prevent GetRecentURLFromClipboard from returning anything until the
   // clipboard's content changed.
   virtual void SuppressClipboardContent() = 0;
 
-  // Sets which URL scheme this app can be opened with. Used by
-  // ClipboardRecentContent to determine whether or not the clipboard contains
-  // a relevant URL. |application_scheme| may be empty.
-  void set_application_scheme(const std::string& application_scheme) {
-    application_scheme_ = application_scheme;
-  }
-
- protected:
-  ClipboardRecentContent() {}
-  virtual ~ClipboardRecentContent() {}
-  // Contains the URL scheme opening the app. May be empty.
-  std::string application_scheme_;
-
  private:
   DISALLOW_COPY_AND_ASSIGN(ClipboardRecentContent);
 };
 
 #endif  // COMPONENTS_OPEN_FROM_CLIPBOARD_CLIPBOARD_RECENT_CONTENT_H_