[Sync] Remove static methods on SyncedWindowDelegate.

chrome/browser/sync/sessions/synced_window_delegates_getter.h

 // Copyright 2014 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_SYNC_SESSIONS_SYNCED_WINDOW_DELEGATES_GETTER_H_
 #define CHROME_BROWSER_SYNC_SESSIONS_SYNCED_WINDOW_DELEGATES_GETTER_H_
 
 #include <set>
+
 #include "base/macros.h"
+#include "components/sessions/session_id.h"
 
 namespace browser_sync {
 
 class SyncedWindowDelegate;
 
+// An interface for accessing SyncedWindowDelegates. Subclasses define
+// how this is done on different platforms.
 class SyncedWindowDelegatesGetter {
  public:
   SyncedWindowDelegatesGetter();
   virtual ~SyncedWindowDelegatesGetter();
-  virtual std::set<const SyncedWindowDelegate*> GetSyncedWindowDelegates();
+
+  // Returns all SyncedWindowDelegate instances.
+  virtual std::set<const SyncedWindowDelegate*> GetSyncedWindowDelegates() = 0;
+
+  // Find a SyncedWindowDelegate given its window's id.
+  virtual const SyncedWindowDelegate* FindById(SessionID::id_type id) = 0;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(SyncedWindowDelegatesGetter);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_SESSIONS_SYNCED_WINDOW_DELEGATES_GETTER_H_