Update server-backed state key generation.

chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h

Index: chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h
diff --git a/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h b/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h
index c8d5f489ab1eda2d1cf00bf9c6ae25a2f6a7b0d1..269673d1da3d8dac90be66bcedcf7615945673a7 100644
--- a/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h
+++ b/chrome/browser/chromeos/policy/device_cloud_policy_manager_chromeos.h
@@ -7,6 +7,7 @@
 
 #include <bitset>
 #include <string>
+#include <vector>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
@@ -45,6 +46,17 @@ class DeviceCloudPolicyManagerChromeOS : public CloudPolicyManager {
   typedef std::bitset<32> AllowedDeviceModes;
   typedef base::Callback<void(EnrollmentStatus)> EnrollmentCallback;
 
+  // The power of two determining the size of the time quanta for device state
+  // keys, i.e. the quanta will be of size 2^kDeviceStateKeyTimeQuantumPower
+  // seconds. 2^23 seconds corresponds to 97.09 days.
+  static const int kDeviceStateKeyTimeQuantumPower = 23;
+
+  // The number of future time quanta to generate device state identifiers for.
+  // This determines the interval after which a device will no longer receive
+  // server-backed state information and thus corresponds to the delay until a
+  // device becomes anonymous to the server again.

[Joao da Silva, 2014/03/27 15:45:40]

If I understood the implementation correctly then it will take about 5*97 days
== 40 months until the device becomes anonymous to the server again. Is that
what's intended?

Can you expand this comment to describe how this interval can be derived from
these 2 values?

[Mattias Nissler (ping if slow), 2014/03/27 16:12:41]

5 * 97 is closer to 16 months :) The goal was one year, so that's 4 quanta. Then
we add one to make up for the fact that the current quantum might be almost
over, yielding the magic 5 number here.
Updated the comment.

+  static const int kDeviceStateKeyFutureQuanta = 5;
+
   // |task_runner| is the runner for policy refresh tasks.
   // |background_task_runner| is used to execute long-running background tasks
   // that may involve file I/O.
@@ -101,8 +113,14 @@ class DeviceCloudPolicyManagerChromeOS : public CloudPolicyManager {
   // Returns the machine model, or an empty string if not available.
   static std::string GetMachineModel();
 
-  // Returns the stable device state key.
-  static std::string GetDeviceStateKey();
+  // Gets the device state keys for |timestamp|. These will cover a time frame
+  // including |timestamp| and extending into the future as configured by the
+  // constants declared above.
+  static bool GetDeviceStateKeys(const base::Time& timestamp,
+                                 std::vector<std::string>* state_keys);
+
+  // Returns the currently valid device state key.
+  static std::string GetCurrentDeviceStateKey();
 
   // Returns the robot 'email address' associated with the device robot
   // account (sometimes called a service account) associated with this device