Break extensions ProcessManager dependency on Runtime API

extensions/browser/process_manager_observer.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 EXTENSIONS_BROWSER_PROCESS_MANAGER_OBSERVER_H_
+#define EXTENSIONS_BROWSER_PROCESS_MANAGER_OBSERVER_H_
+
+namespace extensions {
+class Extension;
+
+class ProcessManagerObserver {
+ public:
+  virtual ~ProcessManagerObserver() {}
+
+  // Called immediately after an extension background host is started.
+  virtual void OnBackgroundHostStartup(const Extension* extension) = 0;
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_PROCESS_MANAGER_OBSERVER_H_