Introduce AppsClient and use it in apps to get the loaded profiles list.

apps/apps_client.h

+// Copyright 2013 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 APPS_APPS_CLIENT_H_
+#define APPS_APPS_CLIENT_H_
+
+#include <vector>
+
+namespace content {
+class BrowserContext;
+}
+
+namespace apps {
+
+// Sets up global state for the apps system. Should be Set() once in each
+// process. This should be implemented by the client of the apps system.
+class AppsClient {
+ public:
+  // Get all loaded browser contexts.
+  virtual std::vector<content::BrowserContext*> GetLoadedBrowserContexts() = 0;
+
+  // Return the apps client.
+  static AppsClient* Get();
+
+  // Initialize the apps system with this apps client.
+  static void Set(AppsClient* client);
+};
+
+}  // namespace apps
+
+#endif  // APPS_APPS_CLIENT_H_