Refactor SyncBackendHost

chrome/browser/sync/glue/sync_backend_host.h

 // Copyright (c) 2012 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_SYNC_GLUE_SYNC_BACKEND_HOST_H_
 #define CHROME_BROWSER_SYNC_GLUE_SYNC_BACKEND_HOST_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/compiler_specific.h"
-#include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
-#include "base/memory/weak_ptr.h"
 #include "base/threading/thread.h"
-#include "chrome/browser/invalidation/invalidation_service.h"
 #include "chrome/browser/sync/glue/backend_data_type_configurer.h"
-#include "chrome/browser/sync/glue/extensions_activity_monitor.h"
-#include "content/public/browser/notification_observer.h"
-#include "content/public/browser/notification_registrar.h"
-#include "google_apis/gaia/google_service_auth_error.h"
 #include "sync/internal_api/public/base/model_type.h"
 #include "sync/internal_api/public/configure_reason.h"
-#include "sync/internal_api/public/engine/model_safe_worker.h"
 #include "sync/internal_api/public/sessions/sync_session_snapshot.h"
-#include "sync/internal_api/public/sync_encryption_handler.h"
 #include "sync/internal_api/public/sync_manager.h"
 #include "sync/internal_api/public/util/report_unrecoverable_error_function.h"
 #include "sync/internal_api/public/util/unrecoverable_error_handler.h"
 #include "sync/internal_api/public/util/weak_handle.h"
-#include "sync/notifier/invalidation_handler.h"
-#include "sync/protocol/encryption.pb.h"
-#include "sync/protocol/sync_protocol_error.h"
-#include "sync/util/extensions_activity.h"
-#include "url/gurl.h"
 
-class Profile;
+class GURL;
 
 namespace base {
 class MessageLoop;
 }
 
 namespace syncer {
 class SyncManagerFactory;
 }
 
 namespace browser_sync {
 
 class ChangeProcessor;
-class InvalidatorStorage;
-class SyncBackendRegistrar;
-class SyncPrefs;
+class SyncFrontend;
 class SyncedDeviceTracker;
-struct Experiments;
 
-// SyncFrontend is the interface used by SyncBackendHost to communicate with
-// the entity that created it and, presumably, is interested in sync-related
-// activity.
-// NOTE: All methods will be invoked by a SyncBackendHost on the same thread
-// used to create that SyncBackendHost.
-class SyncFrontend {
- public:
-  SyncFrontend() {}
-
-  // The backend has completed initialization and it is now ready to
-  // accept and process changes.  If success is false, initialization
-  // wasn't able to be completed and should be retried.
-  //
-  // |js_backend| is what about:sync interacts with; it's different
-  // from the 'Backend' in 'OnBackendInitialized' (unfortunately).  It
-  // is initialized only if |success| is true.
-  virtual void OnBackendInitialized(
-      const syncer::WeakHandle<syncer::JsBackend>& js_backend,
-      const syncer::WeakHandle<syncer::DataTypeDebugInfoListener>&
-          debug_info_listener,
-      bool success) = 0;
-
-  // The backend queried the server recently and received some updates.
-  virtual void OnSyncCycleCompleted() = 0;
-
-  // Configure ran into some kind of error. But it is scheduled to be
-  // retried.
-  virtual void OnSyncConfigureRetry() = 0;
-
-  // The status of the connection to the sync server has changed.
-  virtual void OnConnectionStatusChange(
-      syncer::ConnectionStatus status) = 0;
-
-  // We are no longer permitted to communicate with the server. Sync should
-  // be disabled and state cleaned up at once.
-  virtual void OnStopSyncingPermanently() = 0;
-
-  // The syncer requires a passphrase to decrypt sensitive updates. This is
-  // called when the first sensitive data type is setup by the user and anytime
-  // the passphrase is changed by another synced client. |reason| denotes why
-  // the passphrase was required. |pending_keys| is a copy of the
-  // cryptographer's pending keys to be passed on to the frontend in order to
-  // be cached.
-  virtual void OnPassphraseRequired(
-      syncer::PassphraseRequiredReason reason,
-      const sync_pb::EncryptedData& pending_keys) = 0;
-
-  // Called when the passphrase provided by the user is
-  // accepted. After this is called, updates to sensitive nodes are
-  // encrypted using the accepted passphrase.
-  virtual void OnPassphraseAccepted() = 0;
-
-  // Called when the set of encrypted types or the encrypt everything
-  // flag has been changed.  Note that encryption isn't complete until
-  // the OnEncryptionComplete() notification has been sent (see
-  // below).
-  //
-  // |encrypted_types| will always be a superset of
-  // syncer::Cryptographer::SensitiveTypes().  If |encrypt_everything| is
-  // true, |encrypted_types| will be the set of all known types.
-  //
-  // Until this function is called, observers can assume that the set
-  // of encrypted types is syncer::Cryptographer::SensitiveTypes() and that
-  // the encrypt everything flag is false.
-  virtual void OnEncryptedTypesChanged(
-      syncer::ModelTypeSet encrypted_types,
-      bool encrypt_everything) = 0;
-
-  // Called after we finish encrypting the current set of encrypted
-  // types.
-  virtual void OnEncryptionComplete() = 0;
-
-  // Called to perform migration of |types|.
-  virtual void OnMigrationNeededForTypes(syncer::ModelTypeSet types) = 0;
-
-  // Inform the Frontend that new datatypes are available for registration.
-  virtual void OnExperimentsChanged(
-      const syncer::Experiments& experiments) = 0;
-
-  // Called when the sync cycle returns there is an user actionable error.
-  virtual void OnActionableError(const syncer::SyncProtocolError& error) = 0;
-
- protected:
-  // Don't delete through SyncFrontend interface.
-  virtual ~SyncFrontend() {
-  }
- private:
-  DISALLOW_COPY_AND_ASSIGN(SyncFrontend);
-};
-
-// A UI-thread safe API into the sync backend that "hosts" the top-level
-// syncapi element, the SyncManager, on its own thread. This class handles
-// dispatch of potentially blocking calls to appropriate threads and ensures
-// that the SyncFrontend is only accessed on the UI loop.
-class SyncBackendHost
-    : public BackendDataTypeConfigurer,
-      public content::NotificationObserver,
-      public syncer::InvalidationHandler {
+// An API to "host" the top level syncapi element.

[Nicolas Zea, 2013/11/06 18:03:21]

nit: syncapi -> SyncAPI

Also , typically the interface itself is the class that documents what the
virtual methods are all supposed to be doing. I think I prefer that approach,
which then allows you to let the impl just have a comment saying
"SyncBackendHost implementation" for all the overridden elements.

[rlarocque, 2013/11/06 21:48:47]

Done.

+//
+// See SyncBackendHostImpl for documentation.
+class SyncBackendHost : public BackendDataTypeConfigurer {
  public:
   typedef syncer::SyncStatus Status;
 
-  // Create a SyncBackendHost with a reference to the |frontend| that
-  // it serves and communicates to via the SyncFrontend interface (on
-  // the same thread it used to call the constructor).  Must outlive
-  // |sync_prefs| and |invalidator_storage|.
-  SyncBackendHost(
-      const std::string& name,
-      Profile* profile,
-      const base::WeakPtr<SyncPrefs>& sync_prefs);
+  SyncBackendHost();
+  virtual ~SyncBackendHost() = 0;

[Nicolas Zea, 2013/11/06 18:03:21]

This shouldn't be purely virtual

[rlarocque, 2013/11/06 21:48:47]

Why?

[Nicolas Zea, 2013/11/06 22:18:25]

Because it's kind of confusing and against the style guide. A purely virtual
destructor doesn't really mean much. You still have to define it. And our style
guide already requires all destructors to be virtual.

See http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml#Interfaces

[rlarocque, 2013/11/06 22:48:47]

OK.  Fixed.

 
-  // For testing.
-  // TODO(skrul): Extract an interface so this is not needed.
-  explicit SyncBackendHost(Profile* profile);
-  virtual ~SyncBackendHost();
-
-  // Called on |frontend_loop_| to kick off asynchronous initialization.
-  // As a fallback when no cached auth information is available, try to
-  // bootstrap authentication using |lsid|, if it isn't empty.
-  // Optionally delete the Sync Data folder (if it's corrupt).
-  // |report_unrecoverable_error_function| can be NULL.
-  // Note: |unrecoverable_error_handler| may be invoked from any thread.
-  void Initialize(
+  virtual void Initialize(
       SyncFrontend* frontend,
       scoped_ptr<base::Thread> sync_thread,
       const syncer::WeakHandle<syncer::JsEventHandler>& event_handler,
       const GURL& service_url,
       const syncer::SyncCredentials& credentials,
       bool delete_sync_data_folder,
       scoped_ptr<syncer::SyncManagerFactory> sync_manager_factory,
       scoped_ptr<syncer::UnrecoverableErrorHandler> unrecoverable_error_handler,
       syncer::ReportUnrecoverableErrorFunction
-          report_unrecoverable_error_function);
+          report_unrecoverable_error_function) = 0;
 
-  // Called on |frontend_loop| to update SyncCredentials.
-  virtual void UpdateCredentials(const syncer::SyncCredentials& credentials);
+  virtual void UpdateCredentials(
+      const syncer::SyncCredentials& credentials) = 0;
 
-  // This starts the SyncerThread running a Syncer object to communicate with
-  // sync servers.  Until this is called, no changes will leave or enter this
-  // browser from the cloud / sync servers.
-  // Called on |frontend_loop_|.
-  virtual void StartSyncingWithServer();
+  virtual void StartSyncingWithServer() = 0;
 
-  // Called on |frontend_loop_| to asynchronously set a new passphrase for
-  // encryption. Note that it is an error to call SetEncryptionPassphrase under
-  // the following circumstances:
-  // - An explicit passphrase has already been set
-  // - |is_explicit| is true and we have pending keys.
-  // When |is_explicit| is false, a couple of things could happen:
-  // - If there are pending keys, we try to decrypt them. If decryption works,
-  //   this acts like a call to SetDecryptionPassphrase. If not, the GAIA
-  //   passphrase passed in is cached so we can re-encrypt with it in future.
-  // - If there are no pending keys, data is encrypted with |passphrase| (this
-  //   is a no-op if data was already encrypted with |passphrase|.)
-  void SetEncryptionPassphrase(const std::string& passphrase, bool is_explicit);
+  virtual void SetEncryptionPassphrase(
+      const std::string& passphrase,
+      bool is_explicit) = 0;
+  virtual bool SetDecryptionPassphrase(const std::string& passphrase)
+      WARN_UNUSED_RESULT = 0;
 
-  // Called on |frontend_loop_| to use the provided passphrase to asynchronously
-  // attempt decryption. Returns false immediately if the passphrase could not
-  // be used to decrypt a locally cached copy of encrypted keys; returns true
-  // otherwise. If new encrypted keys arrive during the asynchronous call,
-  // OnPassphraseRequired may be triggered at a later time. It is an error to
-  // call this when there are no pending keys.
-  bool SetDecryptionPassphrase(const std::string& passphrase)
-      WARN_UNUSED_RESULT;
-
-  // Called on |frontend_loop_| to kick off shutdown procedure.  Attempts to cut
-  // short any long-lived or blocking sync thread tasks so that the shutdown on
-  // sync thread task that we're about to post won't have to wait very long.
-  virtual void StopSyncingForShutdown();
-
-  // Called on |frontend_loop_| to kick off shutdown.
-  // See the implementation and Core::DoShutdown for details.
-  // Must be called *after* StopSyncingForShutdown. Caller should claim sync
-  // thread using STOP_AND_CLAIM_THREAD or DISABLE_AND_CLAIM_THREAD if sync
-  // backend might be recreated later because otherwise:
-  // * sync loop may be stopped on main loop and cause it to be blocked.
-  // * new/old backend may interfere with each other if new backend is created
-  //   before old one finishes cleanup.
+  virtual void StopSyncingForShutdown() = 0;
   enum ShutdownOption {
     STOP,                      // Stop syncing and let backend stop sync thread.
     STOP_AND_CLAIM_THREAD,     // Stop syncing and return sync thread.
     DISABLE_AND_CLAIM_THREAD,  // Disable sync and return sync thread.
   };
-  scoped_ptr<base::Thread> Shutdown(ShutdownOption option);
+  virtual scoped_ptr<base::Thread> Shutdown(ShutdownOption option) = 0;
 
-  // Removes all current registrations from the backend on the
-  // InvalidationService.
-  void UnregisterInvalidationIds();
+  virtual void UnregisterInvalidationIds() = 0;
 
-  // Changes the set of data types that are currently being synced.
-  // The ready_task will be run when configuration is done with the
-  // set of all types that failed configuration (i.e., if its argument
-  // is non-empty, then an error was encountered).
   virtual void ConfigureDataTypes(
       syncer::ConfigureReason reason,
       const DataTypeConfigStateMap& config_state_map,
       const base::Callback<void(syncer::ModelTypeSet,
                                 syncer::ModelTypeSet)>& ready_task,
-      const base::Callback<void()>& retry_callback) OVERRIDE;
+      const base::Callback<void()>& retry_callback) OVERRIDE = 0;
 
-  // Turns on encryption of all present and future sync data.
-  virtual void EnableEncryptEverything();
+  virtual void EnableEncryptEverything() = 0;
 
-  // Activates change processing for the given data type.  This must
-  // be called synchronously with the data type's model association so
-  // no changes are dropped between model association and change
-  // processor activation.
-  void ActivateDataType(
+  virtual void ActivateDataType(
       syncer::ModelType type, syncer::ModelSafeGroup group,
-      ChangeProcessor* change_processor);
+      ChangeProcessor* change_processor) = 0;
+  virtual void DeactivateDataType(syncer::ModelType type) = 0;
 
-  // Deactivates change processing for the given data type.
-  void DeactivateDataType(syncer::ModelType type);
+  virtual syncer::UserShare* GetUserShare() const = 0;
 
-  // Called on |frontend_loop_| to obtain a handle to the UserShare needed for
-  // creating transactions.  Should not be called before we signal
-  // initialization is complete with OnBackendInitialized().
-  syncer::UserShare* GetUserShare() const;
+  virtual Status GetDetailedStatus() = 0;
+  virtual syncer::sessions::SyncSessionSnapshot
+      GetLastSessionSnapshot() const = 0;
 
-  // Called from any thread to obtain current status information in detailed or
-  // summarized form.
-  Status GetDetailedStatus();
-  syncer::sessions::SyncSessionSnapshot GetLastSessionSnapshot() const;
+  virtual bool HasUnsyncedItems() const = 0;
 
-  // Determines if the underlying sync engine has made any local changes to
-  // items that have not yet been synced with the server.
-  // ONLY CALL THIS IF OnInitializationComplete was called!
-  bool HasUnsyncedItems() const;
+  virtual bool IsNigoriEnabled() const = 0;
+  virtual syncer::PassphraseType GetPassphraseType() const = 0;
+  virtual base::Time GetExplicitPassphraseTime() const = 0;
+  virtual bool IsCryptographerReady(
+      const syncer::BaseTransaction* trans) const = 0;
 
-  // Whether or not we are syncing encryption keys.
-  bool IsNigoriEnabled() const;
+  virtual void GetModelSafeRoutingInfo(
+      syncer::ModelSafeRoutingInfo* out) const = 0;
 
-  // Returns the type of passphrase being used to encrypt data. See
-  // sync_encryption_handler.h.
-  syncer::PassphraseType GetPassphraseType() const;
+  virtual SyncedDeviceTracker* GetSyncedDeviceTracker() const = 0;
 
-  // If an explicit passphrase is in use, returns the time at which that
-  // passphrase was set (if available).
-  base::Time GetExplicitPassphraseTime() const;
-
-  // True if the cryptographer has any keys available to attempt decryption.
-  // Could mean we've downloaded and loaded Nigori objects, or we bootstrapped
-  // using a token previously received.
-  bool IsCryptographerReady(const syncer::BaseTransaction* trans) const;
-
-  void GetModelSafeRoutingInfo(syncer::ModelSafeRoutingInfo* out) const;
-
-  // Fetches the DeviceInfo tracker.
-  virtual SyncedDeviceTracker* GetSyncedDeviceTracker() const;
-
-  base::MessageLoop* GetSyncLoopForTesting();
-
- protected:
-  // The types and functions below are protected so that test
-  // subclasses can use them.
-  //
-  // TODO(akalin): Figure out a better way for tests to hook into
-  // SyncBackendHost.
-
-  // Utility struct for holding initialization options.
-  struct DoInitializeOptions {
-    DoInitializeOptions(
-        base::MessageLoop* sync_loop,
-        SyncBackendRegistrar* registrar,
-        const syncer::ModelSafeRoutingInfo& routing_info,
-        const std::vector<syncer::ModelSafeWorker*>& workers,
-        const scoped_refptr<syncer::ExtensionsActivity>& extensions_activity,
-        const syncer::WeakHandle<syncer::JsEventHandler>& event_handler,
-        const GURL& service_url,
-        scoped_ptr<syncer::HttpPostProviderFactory> http_bridge_factory,
-        const syncer::SyncCredentials& credentials,
-        const std::string& invalidator_client_id,
-        scoped_ptr<syncer::SyncManagerFactory> sync_manager_factory,
-        bool delete_sync_data_folder,
-        const std::string& restored_key_for_bootstrapping,
-        const std::string& restored_keystore_key_for_bootstrapping,
-        scoped_ptr<syncer::InternalComponentsFactory>
-            internal_components_factory,
-        scoped_ptr<syncer::UnrecoverableErrorHandler>
-            unrecoverable_error_handler,
-        syncer::ReportUnrecoverableErrorFunction
-            report_unrecoverable_error_function);
-    ~DoInitializeOptions();
-
-    base::MessageLoop* sync_loop;
-    SyncBackendRegistrar* registrar;
-    syncer::ModelSafeRoutingInfo routing_info;
-    std::vector<syncer::ModelSafeWorker*> workers;
-    scoped_refptr<syncer::ExtensionsActivity> extensions_activity;
-    syncer::WeakHandle<syncer::JsEventHandler> event_handler;
-    GURL service_url;
-    // Overridden by tests.
-    scoped_ptr<syncer::HttpPostProviderFactory> http_bridge_factory;
-    syncer::SyncCredentials credentials;
-    const std::string invalidator_client_id;
-    scoped_ptr<syncer::SyncManagerFactory> sync_manager_factory;
-    std::string lsid;
-    bool delete_sync_data_folder;
-    std::string restored_key_for_bootstrapping;
-    std::string restored_keystore_key_for_bootstrapping;
-    scoped_ptr<syncer::InternalComponentsFactory> internal_components_factory;
-    scoped_ptr<syncer::UnrecoverableErrorHandler> unrecoverable_error_handler;
-    syncer::ReportUnrecoverableErrorFunction
-        report_unrecoverable_error_function;
-  };
-
-  // Allows tests to perform alternate core initialization work.
-  virtual void InitCore(scoped_ptr<DoInitializeOptions> options);
-
-  // Request the syncer to reconfigure with the specfied params.
-  // Virtual for testing.
-  virtual void RequestConfigureSyncer(
-      syncer::ConfigureReason reason,
-      syncer::ModelTypeSet to_download,
-      syncer::ModelTypeSet to_purge,
-      syncer::ModelTypeSet to_journal,
-      syncer::ModelTypeSet to_unapply,
-      syncer::ModelTypeSet to_ignore,
-      const syncer::ModelSafeRoutingInfo& routing_info,
-      const base::Callback<void(syncer::ModelTypeSet,
-                                syncer::ModelTypeSet)>& ready_task,
-      const base::Closure& retry_callback);
-
-  // Called when the syncer has finished performing a configuration.
-  void FinishConfigureDataTypesOnFrontendLoop(
-      const syncer::ModelTypeSet enabled_types,
-      const syncer::ModelTypeSet succeeded_configuration_types,
-      const syncer::ModelTypeSet failed_configuration_types,
-      const base::Callback<void(syncer::ModelTypeSet,
-                                syncer::ModelTypeSet)>& ready_task);
-
-  // Reports backend initialization success.  Includes some objects from sync
-  // manager initialization to be passed back to the UI thread.
-  virtual void HandleInitializationSuccessOnFrontendLoop(
-    const syncer::WeakHandle<syncer::JsBackend> js_backend,
-    const syncer::WeakHandle<syncer::DataTypeDebugInfoListener>
-        debug_info_listener);
-
-  // Downloading of control types failed and will be retried. Invokes the
-  // frontend's sync configure retry method.
-  void HandleControlTypesDownloadRetry();
-
-  SyncFrontend* frontend() { return frontend_; }
-
- private:
-  // The real guts of SyncBackendHost, to keep the public client API clean.
-  class Core;
-
-  // An enum representing the steps to initializing the SyncBackendHost.
-  enum InitializationState {
-    NOT_ATTEMPTED,
-    CREATING_SYNC_MANAGER,     // We're waiting for the first callback from the
-                               // sync thread to inform us that the sync
-                               // manager has been created.
-    NOT_INITIALIZED,           // Initialization hasn't completed, but we've
-                               // constructed a SyncManager.
-    INITIALIZATING_CONTROL_TYPES,  // Downloading control types and
-                               // initializing their handlers.
-    INITIALIZED,               // Initialization is complete.
-  };
-
-  // Checks if we have received a notice to turn on experimental datatypes
-  // (via the nigori node) and informs the frontend if that is the case.
-  // Note: it is illegal to call this before the backend is initialized.
-  void AddExperimentalTypes();
-
-  // Handles backend initialization failure.
-  void HandleInitializationFailureOnFrontendLoop();
-
-  // Called from Core::OnSyncCycleCompleted to handle updating frontend
-  // thread components.
-  void HandleSyncCycleCompletedOnFrontendLoop(
-      const syncer::sessions::SyncSessionSnapshot& snapshot);
-
-  // Called when the syncer failed to perform a configuration and will
-  // eventually retry. FinishingConfigurationOnFrontendLoop(..) will be called
-  // on successful completion.
-  void RetryConfigurationOnFrontendLoop(const base::Closure& retry_callback);
-
-  // Helpers to persist a token that can be used to bootstrap sync encryption
-  // across browser restart to avoid requiring the user to re-enter their
-  // passphrase.  |token| must be valid UTF-8 as we use the PrefService for
-  // storage.
-  void PersistEncryptionBootstrapToken(
-      const std::string& token,
-      syncer::BootstrapTokenType token_type);
-
-  // For convenience, checks if initialization state is INITIALIZED.
-  bool initialized() const { return initialized_; }
-
-  // Let the front end handle the actionable error event.
-  void HandleActionableErrorEventOnFrontendLoop(
-      const syncer::SyncProtocolError& sync_error);
-
-  // Checks if |passphrase| can be used to decrypt the cryptographer's pending
-  // keys that were cached during NotifyPassphraseRequired. Returns true if
-  // decryption was successful. Returns false otherwise. Must be called with a
-  // non-empty pending keys cache.
-  bool CheckPassphraseAgainstCachedPendingKeys(
-      const std::string& passphrase) const;
-
-  // Invoked when a passphrase is required to decrypt a set of Nigori keys,
-  // or for encrypting. |reason| denotes why the passphrase was required.
-  // |pending_keys| is a copy of the cryptographer's pending keys, that are
-  // cached by the frontend. If there are no pending keys, or if the passphrase
-  // required reason is REASON_ENCRYPTION, an empty EncryptedData object is
-  // passed.
-  void NotifyPassphraseRequired(syncer::PassphraseRequiredReason reason,
-                                sync_pb::EncryptedData pending_keys);
-
-  // Invoked when the passphrase provided by the user has been accepted.
-  void NotifyPassphraseAccepted();
-
-  // Invoked when the set of encrypted types or the encrypt
-  // everything flag changes.
-  void NotifyEncryptedTypesChanged(
-      syncer::ModelTypeSet encrypted_types,
-      bool encrypt_everything);
-
-  // Invoked when sync finishes encrypting new datatypes.
-  void NotifyEncryptionComplete();
-
-  // Invoked when the passphrase state has changed. Caches the passphrase state
-  // for later use on the UI thread.
-  // If |type| is FROZEN_IMPLICIT_PASSPHRASE or CUSTOM_PASSPHRASE,
-  // |explicit_passphrase_time| is the time at which that passphrase was set
-  // (if available).
-  void HandlePassphraseTypeChangedOnFrontendLoop(
-      syncer::PassphraseType type,
-      base::Time explicit_passphrase_time);
-
-  void HandleStopSyncingPermanentlyOnFrontendLoop();
-
-  // Dispatched to from OnConnectionStatusChange to handle updating
-  // frontend UI components.
-  void HandleConnectionStatusChangeOnFrontendLoop(
-      syncer::ConnectionStatus status);
-
-  // syncer::InvalidationHandler-like functions.
-  void HandleInvalidatorStateChangeOnFrontendLoop(
-      syncer::InvalidatorState state);
-  void HandleIncomingInvalidationOnFrontendLoop(
-      const syncer::ObjectIdInvalidationMap& invalidation_map);
-
-  // NotificationObserver implementation.
-  virtual void Observe(
-    int type,
-    const content::NotificationSource& source,
-    const content::NotificationDetails& details) OVERRIDE;
-
-  // InvalidationHandler implementation.
-  virtual void OnInvalidatorStateChange(
-      syncer::InvalidatorState state) OVERRIDE;
-  virtual void OnIncomingInvalidation(
-      const syncer::ObjectIdInvalidationMap& invalidation_map) OVERRIDE;
-
-  content::NotificationRegistrar notification_registrar_;
-
-  // A reference to the MessageLoop used to construct |this|, so we know how
-  // to safely talk back to the SyncFrontend.
-  base::MessageLoop* const frontend_loop_;
-
-  Profile* const profile_;
-
-  // Name used for debugging (set from profile_->GetDebugName()).
-  const std::string name_;
-
-  // Our core, which communicates directly to the syncapi. Use refptr instead
-  // of WeakHandle because |core_| is created on UI loop but released on
-  // sync loop.
-  scoped_refptr<Core> core_;
-
-  bool initialized_;
-
-  const base::WeakPtr<SyncPrefs> sync_prefs_;
-
-  ExtensionsActivityMonitor extensions_activity_monitor_;
-
-  scoped_ptr<SyncBackendRegistrar> registrar_;
-
-  // The frontend which we serve (and are owned by).
-  SyncFrontend* frontend_;
-
-  // We cache the cryptographer's pending keys whenever NotifyPassphraseRequired
-  // is called. This way, before the UI calls SetDecryptionPassphrase on the
-  // syncer, it can avoid the overhead of an asynchronous decryption call and
-  // give the user immediate feedback about the passphrase entered by first
-  // trying to decrypt the cached pending keys on the UI thread. Note that
-  // SetDecryptionPassphrase can still fail after the cached pending keys are
-  // successfully decrypted if the pending keys have changed since the time they
-  // were cached.
-  sync_pb::EncryptedData cached_pending_keys_;
-
-  // The state of the passphrase required to decrypt the bag of encryption keys
-  // in the nigori node. Updated whenever a new nigori node arrives or the user
-  // manually changes their passphrase state. Cached so we can synchronously
-  // check it from the UI thread.
-  syncer::PassphraseType cached_passphrase_type_;
-
-  // If an explicit passphrase is in use, the time at which the passphrase was
-  // first set (if available).
-  base::Time cached_explicit_passphrase_time_;
-
-  // UI-thread cache of the last SyncSessionSnapshot received from syncapi.
-  syncer::sessions::SyncSessionSnapshot last_snapshot_;
-
-  invalidation::InvalidationService* invalidator_;
-  bool invalidation_handler_registered_;
-
-  base::WeakPtrFactory<SyncBackendHost> weak_ptr_factory_;
+  virtual base::MessageLoop* GetSyncLoopForTesting() = 0;
 
   DISALLOW_COPY_AND_ASSIGN(SyncBackendHost);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_SYNC_BACKEND_HOST_H_