Add a test helper class for ExtensionRegistry.

extensions/browser/extension_test_registry_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_EXTENSION_TEST_REGISTRY_OBSERVER_H_
+#define EXTENSIONS_BROWSER_EXTENSION_TEST_REGISTRY_OBSERVER_H_
+
+#include "base/scoped_observer.h"
+#include "content/public/test/test_utils.h"
+#include "extensions/browser/extension_registry_observer.h"
+
+namespace extensions {
+class ExtensionRegistry;
+
+// A helper class that listen for ExtensionRegistry notifications.
+class ExtensionTestRegistryObserver : public ExtensionRegistryObserver {

[Yoyo Zhou, 2014/06/17 02:29:54]

nit: TestExtensionRegistryObserver?

[limasdf, 2014/06/17 17:20:55]

Done.

+ public:
+  explicit ExtensionTestRegistryObserver(ExtensionRegistry* registry);
+  virtual ~ExtensionTestRegistryObserver();
+
+  void WaitForAnyExtensionWillBeInstalled();

[Yoyo Zhou, 2014/06/17 02:29:54]

These should be documented.
What do you think of changing this interface to wait for a specific extension
ID? It seems like in all of our tests that use this right now, there is an
extension ID we can get at. This would make the test more reliable.

[limasdf, 2014/06/17 17:20:55]

Done.

+  void WaitForAnyExtensionUninstalled();
+
+ private:
+  class Waiter;
+
+  // ExtensionRegistryObserver.
+  virtual void OnExtensionWillBeInstalled(
+      content::BrowserContext* browser_context,
+      const Extension* extension,
+      bool is_update,
+      bool from_ephemeral,
+      const std::string& old_name) OVERRIDE;
+  virtual void OnExtensionUninstalled(content::BrowserContext* browser_context,
+                                      const Extension* extension) OVERRIDE;
+
+  scoped_ptr<Waiter> installed_waiter_;

[Yoyo Zhou, 2014/06/17 02:29:54]

should be will_be_uninstalled_ for consistency.

[limasdf, 2014/06/17 17:20:56]

Done.

+  scoped_ptr<Waiter> uninstalled_waiter_;
+
+  ScopedObserver<ExtensionRegistry, ExtensionRegistryObserver>
+      extension_registry_observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(ExtensionTestRegistryObserver);
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_EXTENSION_TEST_REGISTRY_OBSERVER_H_