Build a new TokenCacheService so I can stop using TokenService for something it wasn't designed for.

chrome/browser/extensions/token_cache/token_cache_service.h

+// Copyright (c) 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 CHROME_BROWSER_EXTENSIONS_TOKEN_CACHE_TOKEN_CACHE_SERVICE_H_
+#define CHROME_BROWSER_EXTENSIONS_TOKEN_CACHE_TOKEN_CACHE_SERVICE_H_
+
+#include <map>
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/time.h"
+#include "chrome/browser/profiles/profile_keyed_service.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+
+namespace content {
+class NotificationSource;
+}
+
+class Profile;
+
+namespace extensions {
+
+// This class caches tokens for the current user.  It will clear tokens out
+// when the user logs out or after the specified timeout interval, or when
+// the instance of chrome shuts down.

[asargent_no_longer_on_chrome, 2013/03/12 00:11:31]

We deciding to clear out the token cache when chrome shuts down, did you
consider the case of users of chrome apps who have the app launcher but don't
use chrome as their main browser? There could be workflows where they launch app
A, close it, and then immediately launch app B, and this token will have expired
after A shuts down.

I don't have a great sense for how common this would be or what the cost of
having to re-fetch the token is, but I just wanted to raise the issue for you to
think about. It could very well be the case that it isn't worth the complexity
of saving these to disk across browser session lifetimes.

[Pete Williamson, 2013/03/12 00:39:25]

The token is only used by Push Messaging.  If there is any app installed with
Push Messaging permission, it will keep chrome up even when the user exits.

Also, Michael (on my team) is considering using this cache for the Identity API,
and if he does, he will make it persist to disk.

+class TokenCacheService : public ProfileKeyedService,
+                          public content::NotificationObserver {
+ public:
+  explicit TokenCacheService(Profile* profile);
+  virtual ~TokenCacheService();
+
+  // Store a token for the currently logged in user. We will look it up later by
+  // the name given here, and we will expire the token after the timeout.  For a
+  // timeout of 0, we never expire the token.  After time_to_live expires, the
+  // token will be expired.
+  void StoreToken(const std::string& token_name, const std::string& token_value,
+                  base::TimeDelta time_to_live);
+
+  // Retrieve a token for the currently logged in user.  This returns an empty
+  // string if the token was not found or timed out.
+  std::string RetrieveToken(const std::string& token_name);
+
+  // inherited from NotificationObserver

[asargent_no_longer_on_chrome, 2013/03/12 00:11:31]

nit: capitalize Inherited, and finish sentence with a period.

[Pete Williamson, 2013/03/12 00:39:25]

Done.

+  virtual void Observe(int type,
+                       const content::NotificationSource& source,
+                       const content::NotificationDetails& details) OVERRIDE;
+
+ private:
+  struct TokenCacheData {
+    std::string token;
+    base::Time expiration_time;
+  };
+
+  std::map<std::string, TokenCacheData> token_cache_;

[asargent_no_longer_on_chrome, 2013/03/12 00:11:31]

Would it be worth mentioning in a comment here what the string key is? (I'm
guessing it's the token name?)

[Pete Williamson, 2013/03/12 00:39:25]

Done.

+  content::NotificationRegistrar registrar_;
+  const Profile* const profile_;
+
+  friend class TokenCacheTest;

[asargent_no_longer_on_chrome, 2013/03/12 00:11:31]

nit: I don't think this is a hard rule in the style guide, but I think a lot of
chrome code, at least in the extensions system, tends to put friend declarations
just after the private: label instead of at the bottom. 

[Pete Williamson, 2013/03/12 00:39:25]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(TokenCacheService);
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_TOKEN_CACHE_TOKEN_CACHE_SERVICE_H_