[CrOS MultiDevice] Fix DeviceReenroller by using DeviceSyncClient::Observer callbacks

The current implementation of DeviceReenroller uses the incorrect
callbacks to signal when an enrollment and device sync are complete.
Specifically, the ForceEnrollmentNow() and ForceSyncNow() callbacks were
used instead of the DeviceSyncClient::Observer callbacks,
OnEnrollmentFinished() and OnNewDevicesSynced().

Here, we use to the correct callbacks along with a more appropriate and
simplified retry mechanism. Namely, the complete re-enrollment
process of enrollment --> device sync --> verification is retried every
5 minutes or until success.

Note: The OnEnrollmentFinished() and OnNewDevicesSynced() callbacks
might be invoked due to enrollments or device syncs external to the
DeviceReenroller class. Regardless of how the functions are called, the
two sets of supported software features (from GCM device info and local
device metadata) are compared. If they disagree, the re-enrollment
process is triggered.

Bug: 870770
Change-Id: If33320386cd8ce5d5639082009291b935ec6e471
Tested: Manual and unit tests
Reviewed-on: https://chromium-review.googlesource.com/1228311
Commit-Queue: Josh Nohle <nohle@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592816}

chromeos/services/multidevice_setup/BUILD.gn

@@ -62,6 +62,7 @@ static_library("multidevice_setup") {
     "//chromeos/services/secure_channel/public/cpp/client",
     "//chromeos/services/secure_channel/public/mojom",
     "//components/cryptauth",
+    "//components/cryptauth/proto:util",
     "//components/pref_registry",
     "//components/prefs:prefs",
     "//services/service_manager/public/cpp",

chromeos/services/multidevice_setup/device_reenroller.h

@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "base/macros.h"
+#include "chromeos/services/device_sync/public/cpp/device_sync_client.h"
 #include "components/cryptauth/proto/cryptauth_api.pb.h"
 
 namespace base {
@@ -20,16 +21,37 @@ class GcmDeviceInfoProvider;
 
 namespace chromeos {
 
-namespace device_sync {
-class DeviceSyncClient;
-}  // namespace device_sync
-
 namespace multidevice_setup {
 
-// The DeviceReenroller constructor re-enrolls and syncs the device if the set
-// of supported SoftwareFeatures in the current GCM device info differs from
-// that of the local device metadata on the CryptAuth server.
-class DeviceReenroller {
+// This class re-enrolls the device if the set of supported SoftwareFeatures in
+// the GCM device info differs from that of the local device metadata. This
+// condition is checked in the constructor and any time the
+// DeviceSyncClient::Observer callbacks--OnEnrollmentFinished() and
+// OnNewDevicesSync()--are called.
+//
+// The supported software features listed in GCM device info should be
+// considered the new source of truth. Enrollment updates a device's list of
+// supported software features (among other things) on the backend to conform
+// with the GCM device info. Then, a device sync is necessary to update the
+// cache of device information with the latest backend data. The local device
+// metadata is part of this cache.
+//
+// The flow of the class is as follows:
+//
+//   +-------------------------------------------------------------------------+
+//   |                                                                         |
+//   |              (From external enrollment)      (From external device sync)|
+//   |                         |                                    |          |
+//   V                         V                                    V          |
+// Start-->Enrollment-->OnEnrollmentFinished-->DeviceSync-->OnNewDevicesSynced-+
+//   |                         |
+//   |                         |
+//   V                         V
+//   If features agree, then done
+//
+// A five-minute retry timer is started at the beginning of the flow. Should any
+// step fail, the process will be re-started when the timer fires.
+class DeviceReenroller : public device_sync::DeviceSyncClient::Observer {
  public:
   class Factory {
    public:
@@ -46,7 +68,7 @@ class DeviceReenroller {
     static Factory* test_factory_;
   };
 
-  virtual ~DeviceReenroller();
+  ~DeviceReenroller() override;
 
  private:
   DeviceReenroller(
@@ -54,22 +76,18 @@ class DeviceReenroller {
       const cryptauth::GcmDeviceInfoProvider* gcm_device_info_provider,
       std::unique_ptr<base::OneShotTimer> timer);
 
-  void AttemptReenrollment();
-  void AttemptDeviceSync();
+  void AttemptReenrollmentIfNecessary();
+  // Returns a sorted and deduped list of the supported or enabled software
+  // features from DeviceSyncClient::GetLocalDeviceMetadata().
+  std::vector<cryptauth::SoftwareFeature> GetSupportedFeaturesForLocalDevice();
 
-  // If the re-enrollment was successful, force a device sync; otherwise, retry
-  // re-enrollment every 5 minutes or until success.
-  void OnForceEnrollmentNowComplete(bool success);
-  // If the device sync was successful and the list of supported software
-  // features on the CryptAuth server now agrees with the list of supported
-  // software features in GcmDeviceInfo, log the success; otherwise, retry
-  // device sync every 5 minutes or until success.
-  void OnForceSyncNowComplete(bool success);
+  // device_sync::DeviceSyncClient::Observer:
+  void OnEnrollmentFinished() override;
+  void OnNewDevicesSynced() override;
 
   device_sync::DeviceSyncClient* device_sync_client_;
-  // The sorted and deduped list of supported software features extracted from
-  // GcmDeviceInfo.
-  std::vector<cryptauth::SoftwareFeature> gcm_supported_software_features_;
+  const std::vector<cryptauth::SoftwareFeature>
+      gcm_supported_software_features_;
   std::unique_ptr<base::OneShotTimer> timer_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceReenroller);