Introduce NonBlockingDataTypeController

The NonBlockingDataTypeController tracks the sync state of
a non-blocking data type and sends signals to its components from the UI
thread.  It is responsible for enabling and disabling sync for a data
type according to user preference and the availbility of the sync
backend.

This CL also includes some changes to the NonBlockingDataTypeProcessor,
which is currently just a stub of what will eventually become
non-blocking sync's model thread component, so that it can be used in
testing NonBlockingDataTypeController.

BUG=351005

Review URL: https://codereview.chromium.org/249843002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@266344 0039d316-1c4b-4281-b951-d872f2087c98

8 files changed, 554 insertions, 16 deletions

diff --git a/components/components_tests.gyp b/components/components_tests.gyp
index b533cd4..a1f587a 100644
--- a/components/components_tests.gyp
+++ b/components/components_tests.gyp
@@ -135,6 +135,7 @@
             'storage_monitor/storage_monitor_win_unittest.cc',
             'sync_driver/generic_change_processor_unittest.cc',
             'sync_driver/model_association_manager_unittest.cc',
+            'sync_driver/non_blocking_data_type_controller_unittest.cc',
             'sync_driver/sync_prefs_unittest.cc',
             'sync_driver/system_encryptor_unittest.cc',
             'test/run_all_unittests.cc',
diff --git a/components/sync_driver.gypi b/components/sync_driver.gypi
index 364274dd..0a13f9f 100644
--- a/components/sync_driver.gypi
+++ b/components/sync_driver.gypi
@@ -35,6 +35,8 @@
         'sync_driver/model_association_manager.cc',
         'sync_driver/model_association_manager.h',
         'sync_driver/model_associator.h',
+        'sync_driver/non_blocking_data_type_controller.cc',
+        'sync_driver/non_blocking_data_type_controller.h',
         'sync_driver/pref_names.cc',
         'sync_driver/pref_names.h',
         'sync_driver/proxy_data_type_controller.cc',
diff --git a/components/sync_driver/non_blocking_data_type_controller.cc b/components/sync_driver/non_blocking_data_type_controller.cc
new file mode 100644
index 0000000..e2e0366
--- /dev/null
+++ b/components/sync_driver/non_blocking_data_type_controller.cc
@@ -0,0 +1,137 @@
+// 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.
+
+#include "components/sync_driver/non_blocking_data_type_controller.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/location.h"
+#include "sync/internal_api/public/non_blocking_type_processor.h"
+
+namespace browser_sync {
+
+NonBlockingDataTypeController::NonBlockingDataTypeController(
+    syncer::ModelType type, bool is_preferred)
+    : type_(type),
+      current_state_(DISCONNECTED),
+      is_preferred_(is_preferred) {}
+
+NonBlockingDataTypeController::~NonBlockingDataTypeController() {}
+
+void NonBlockingDataTypeController::InitializeProcessor(
+      scoped_refptr<base::SequencedTaskRunner> task_runner,
+      base::WeakPtr<syncer::NonBlockingTypeProcessor> processor) {
+  DCHECK(!IsTypeProcessorConnected());
+  task_runner_ = task_runner;
+  processor_ = processor;
+  DCHECK(IsTypeProcessorConnected());
+
+  UpdateState();
+}
+
+void NonBlockingDataTypeController::InitializeSyncCoreProxy(
+    scoped_ptr<syncer::SyncCoreProxy> proxy) {
+  DCHECK(!IsSyncBackendConnected());
+  proxy_ = proxy.Pass();
+
+  UpdateState();
+}
+
+void NonBlockingDataTypeController::ClearSyncCoreProxy() {
+  // Never had a sync core proxy to begin with.  No change.
+  if (!proxy_)
+    return;
+  proxy_.reset();
+
+  UpdateState();
+}
+
+void NonBlockingDataTypeController::SetIsPreferred(bool is_preferred) {
+  is_preferred_ = is_preferred;
+
+  UpdateState();
+}
+
+void NonBlockingDataTypeController::UpdateState() {
+  // Return immediately if no updates are necessary.
+  if (GetDesiredState() == current_state_) {
+    return;
+  }
+
+  // Return immediately if the processor is not ready yet.
+  if (!IsTypeProcessorConnected()) {
+    return;
+  }
+
+  // Send the appropriate state transition request to the processor.
+  switch (GetDesiredState()) {
+    case ENABLED:
+      SendEnableSignal();
+      return;
+    case DISABLED:
+      SendDisableSignal();
+      return;
+    case DISCONNECTED:
+      SendDisconnectSignal();
+      return;
+  }
+  NOTREACHED();
+  return;
+}
+
+void NonBlockingDataTypeController::SendEnableSignal() {
+  DCHECK_EQ(ENABLED, GetDesiredState());
+  DVLOG(1) << "Enabling non-blocking sync type " << ModelTypeToString(type_);
+
+  task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&syncer::NonBlockingTypeProcessor::Enable,
+                 processor_,
+                 base::Owned(proxy_->Clone().release())));
+  current_state_ = ENABLED;
+}
+
+void NonBlockingDataTypeController::SendDisableSignal() {
+  DCHECK_EQ(DISABLED, GetDesiredState());
+  DVLOG(1) << "Disabling non-blocking sync type " << ModelTypeToString(type_);
+  task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&syncer::NonBlockingTypeProcessor::Disable, processor_));
+  current_state_ = DISABLED;
+}
+
+void NonBlockingDataTypeController::SendDisconnectSignal() {
+  DCHECK_EQ(DISCONNECTED, GetDesiredState());
+  DVLOG(1) << "Disconnecting non-blocking sync type "
+           << ModelTypeToString(type_);
+  task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&syncer::NonBlockingTypeProcessor::Disconnect, processor_));
+  current_state_ = DISCONNECTED;
+}
+
+bool NonBlockingDataTypeController::IsPreferred() const {
+  return is_preferred_;
+}
+
+bool NonBlockingDataTypeController::IsTypeProcessorConnected() const {
+  return task_runner_ != NULL;
+}
+
+bool NonBlockingDataTypeController::IsSyncBackendConnected() const {
+  return proxy_;
+}
+
+NonBlockingDataTypeController::TypeProcessorState
+NonBlockingDataTypeController::GetDesiredState() const {
+  if (!IsPreferred()) {
+    return DISABLED;
+  } else if (!IsSyncBackendConnected() || !IsTypeProcessorConnected()) {
+    return DISCONNECTED;
+  } else {
+    return ENABLED;
+  }
+}
+
+}  // namespace browser_sync
diff --git a/components/sync_driver/non_blocking_data_type_controller.h b/components/sync_driver/non_blocking_data_type_controller.h
new file mode 100644
index 0000000..4a1c66c
--- /dev/null
+++ b/components/sync_driver/non_blocking_data_type_controller.h
@@ -0,0 +1,136 @@
+// 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 CHROME_BROWSER_SYNC_NON_BLOCKING_DATA_TYPE_CONTROLLER_H_
+#define CHROME_BROWSER_SYNC_NON_BLOCKING_DATA_TYPE_CONTROLLER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+#include "base/sequenced_task_runner.h"
+#include "sync/internal_api/public/base/model_type.h"
+#include "sync/internal_api/public/sync_core_proxy.h"
+
+namespace syncer {
+class NonBlockingTypeProcessor;
+}
+
+namespace browser_sync {
+
+// Lives on the UI thread and manages the interactions between many sync
+// components.
+//
+// There are three main parts to this controller:
+// - The SyncCoreProxy, represening the sync thread.
+// - The NonBlockingTypeProcessor, representing the model type thread.
+// - The user-set state for this type (prefs), which lives on the UI thread.
+//
+// The NonBlockingSyncTypeProcessor can exist in three different states.  Those
+// states are:
+// - Enabled: Changes are being synced.
+// - Disconnected: Changes would be synced, but there is no connection between
+//                 the sync thread and the model thread.
+// - Disabled: Syncing is intentionally disabled.  The processor may clear any
+//             of its local state associated with sync when this happens, since
+//             this is expected to last a while.
+//
+// This controller is responsible for transitioning the processor into and out
+// of these states.  It does this by posting tasks to the model type thread.
+//
+// The processor is enabled when the user has indicated a desire to sync this
+// type, and the NonBlockingTypeProcessor and SyncCoreProxy are available.
+//
+// The processor is disconnected during initialization, or when either the
+// NonBlockingDataTypeController or SyncCoreProxy have not yet registered.  It
+// can also be disconnected later on if the sync backend becomes unavailable.
+//
+// The processor is disabled if the user has disabled sync for this type.  The
+// signal indicating this state will be sent to the processor when the pref is
+// first changed, or when the processor first connects to the controller.
+//
+// This class is structured using some state machine patterns.  It's a bit
+// awkward at times, but this seems to be the clearest way to express the
+// behaviors this class must implement.
+class NonBlockingDataTypeController {
+ public:
+  NonBlockingDataTypeController(syncer::ModelType type, bool is_preferred);
+  ~NonBlockingDataTypeController();
+
+  // Connects the NonBlockingTypeProcessor to this controller.
+  //
+  // There is no "undo" for this operation.  The NonBlockingDataTypeController
+  // will only ever deal with a single processor.
+  void InitializeProcessor(
+      scoped_refptr<base::SequencedTaskRunner> task_runner,
+      base::WeakPtr<syncer::NonBlockingTypeProcessor> processor);
+
+  // Initialize the connection to the SyncCoreProxy.
+  //
+  // This process may be reversed with ClearSyncCoreProxy().
+  void InitializeSyncCoreProxy(scoped_ptr<syncer::SyncCoreProxy> proxy);
+
+  // Disconnect from the current SyncCoreProxy.
+  void ClearSyncCoreProxy();
+
+  // Sets the current preferred state.
+  //
+  // Represents a choice to sync or not sync this type.  This is expected to
+  // last a long time, so local state may be deleted if this setting is toggled
+  // to false.
+  void SetIsPreferred(bool is_preferred);
+
+ private:
+  enum TypeProcessorState { ENABLED, DISABLED, DISCONNECTED };
+
+  // Figures out which signals need to be sent then send then sends them.
+  void UpdateState();
+
+  // Sends an enable signal to the NonBlockingTypeProcessor.
+  void SendEnableSignal();
+
+  // Sends a disable signal to the NonBlockingTypeProcessor.
+  void SendDisableSignal();
+
+  // Sends a disconnect signal to the NonBlockingTypeProcessor.
+  void SendDisconnectSignal();
+
+  // Returns true if this type should be synced.
+  bool IsPreferred() const;
+
+  // Returns true if this object has access to the NonBlockingTypeProcessor.
+  bool IsTypeProcessorConnected() const;
+
+  // Returns true if this object has access to the SyncCoreProxy.
+  bool IsSyncBackendConnected() const;
+
+  // Returns the state that the processor *should* be in.
+  TypeProcessorState GetDesiredState() const;
+
+  // The ModelType we're controlling.  Kept mainly for debugging.
+  const syncer::ModelType type_;
+
+  // Returns the state that the processor is actually in, from this class'
+  // point of view.
+  //
+  // This state is inferred based on the most recently sent signals, and is
+  // intended to represent the state the processor will be in by the time any
+  // tasks we post to it now will be run.  Due to threading / queueing effects,
+  // this may or may not be the actual state at this point in time.
+  TypeProcessorState current_state_;
+
+  // Whether or not the user wants to sync this type.
+  bool is_preferred_;
+
+  // The NonBlockingTypeProcessor and its associated thread.  May be NULL.
+  scoped_refptr<base::SequencedTaskRunner> task_runner_;
+  base::WeakPtr<syncer::NonBlockingTypeProcessor> processor_;
+
+  // The SyncCoreProxy that connects to the current sync backend.  May be NULL.
+  scoped_ptr<syncer::SyncCoreProxy> proxy_;
+
+  DISALLOW_COPY_AND_ASSIGN(NonBlockingDataTypeController);
+};
+
+}  // namespace browser_sync
+
+#endif  // CHROME_BROWSER_SYNC_NON_BLOCKING_DATA_TYPE_CONTROLLER_H_
diff --git a/components/sync_driver/non_blocking_data_type_controller_unittest.cc b/components/sync_driver/non_blocking_data_type_controller_unittest.cc
new file mode 100644
index 0000000..b695c0b
--- /dev/null
+++ b/components/sync_driver/non_blocking_data_type_controller_unittest.cc
@@ -0,0 +1,227 @@
+// 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.
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/sequenced_task_runner.h"
+#include "base/test/test_simple_task_runner.h"
+#include "components/sync_driver/non_blocking_data_type_controller.h"
+#include "sync/internal_api/public/base/model_type.h"
+#include "sync/internal_api/public/non_blocking_type_processor.h"
+#include "sync/internal_api/public/sync_core_proxy.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace {
+
+class MockSyncCoreProxy : public syncer::SyncCoreProxy {
+ public:
+  MockSyncCoreProxy() {}
+  virtual ~MockSyncCoreProxy() {}
+
+  virtual void ConnectTypeToCore(
+      syncer::ModelType type,
+      base::WeakPtr<syncer::NonBlockingTypeProcessor> type_processor) OVERRIDE {
+    type_processor->OnConnect(
+        base::WeakPtr<syncer::NonBlockingTypeProcessorCore>(),
+        scoped_refptr<base::SequencedTaskRunner>());
+  }
+
+  virtual scoped_ptr<SyncCoreProxy> Clone() OVERRIDE {
+    return scoped_ptr<SyncCoreProxy>(new MockSyncCoreProxy());
+  }
+};
+
+class NonBlockingDataTypeControllerTest : public testing::Test {
+ public:
+  NonBlockingDataTypeControllerTest()
+      : processor_(syncer::DICTIONARY),
+        model_thread_(new base::TestSimpleTaskRunner()),
+        controller_(syncer::DICTIONARY, true) {}
+
+  virtual ~NonBlockingDataTypeControllerTest() {}
+
+  // Connects the processor to the NonBlockingDataTypeController.
+  void InitProcessor() {
+    controller_.InitializeProcessor(
+        model_thread_, processor_.AsWeakPtr());
+    RunQueuedTasks();
+  }
+
+  // Connects the sync backend to the NonBlockingDataTypeController.
+  void InitSync() {
+    controller_.InitializeSyncCoreProxy(mock_core_proxy_.Clone());
+    RunQueuedTasks();
+  }
+
+  // Disconnects the sync backend from the NonBlockingDataTypeController.
+  void UninitializeSync() {
+    controller_.ClearSyncCoreProxy();
+    RunQueuedTasks();
+  }
+
+  // Toggles the user's preference for syncing this type.
+  void SetIsPreferred(bool preferred) {
+    controller_.SetIsPreferred(preferred);
+    RunQueuedTasks();
+  }
+
+  // The processor pretends to run tasks on a different thread.
+  // This function runs any posted tasks.
+  void RunQueuedTasks() {
+    model_thread_->RunUntilIdle();
+  }
+
+ protected:
+  MockSyncCoreProxy mock_core_proxy_;
+
+  syncer::NonBlockingTypeProcessor processor_;
+  scoped_refptr<base::TestSimpleTaskRunner> model_thread_;
+
+  browser_sync::NonBlockingDataTypeController controller_;
+};
+
+// Initialization when the user has disabled syncing for this type.
+TEST_F(NonBlockingDataTypeControllerTest, UserDisabled) {
+  SetIsPreferred(false);
+  InitProcessor();
+  InitSync();
+
+  EXPECT_FALSE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+
+  UninitializeSync();
+
+  EXPECT_FALSE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+}
+
+// Init the sync backend then the type processor.
+TEST_F(NonBlockingDataTypeControllerTest, Enabled_SyncFirst) {
+  SetIsPreferred(true);
+  InitSync();
+  EXPECT_FALSE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+
+  InitProcessor();
+  EXPECT_TRUE(processor_.IsPreferred());
+  EXPECT_TRUE(processor_.IsConnected());
+
+  UninitializeSync();
+  EXPECT_TRUE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+}
+
+// Init the type processor then the sync backend.
+TEST_F(NonBlockingDataTypeControllerTest, Enabled_ProcessorFirst) {
+  SetIsPreferred(true);
+  InitProcessor();
+  EXPECT_FALSE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+
+  InitSync();
+  EXPECT_TRUE(processor_.IsPreferred());
+  EXPECT_TRUE(processor_.IsConnected());
+
+  UninitializeSync();
+  EXPECT_TRUE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+}
+
+// Initialize sync then disable it with a pref change.
+TEST_F(NonBlockingDataTypeControllerTest, PreferThenNot) {
+  SetIsPreferred(true);
+  InitProcessor();
+  InitSync();
+
+  EXPECT_TRUE(processor_.IsPreferred());
+  EXPECT_TRUE(processor_.IsConnected());
+
+  SetIsPreferred(false);
+  EXPECT_FALSE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+}
+
+// Connect type processor and sync backend, then toggle prefs repeatedly.
+TEST_F(NonBlockingDataTypeControllerTest, RepeatedTogglePreference) {
+  SetIsPreferred(false);
+  InitProcessor();
+  InitSync();
+  EXPECT_FALSE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+
+  SetIsPreferred(true);
+  EXPECT_TRUE(processor_.IsPreferred());
+  EXPECT_TRUE(processor_.IsConnected());
+
+  SetIsPreferred(false);
+  EXPECT_FALSE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+
+  SetIsPreferred(true);
+  EXPECT_TRUE(processor_.IsPreferred());
+  EXPECT_TRUE(processor_.IsConnected());
+
+  SetIsPreferred(false);
+  EXPECT_FALSE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+}
+
+// Test sync backend getting restarted while processor is connected.
+TEST_F(NonBlockingDataTypeControllerTest, RestartSyncBackend) {
+  SetIsPreferred(true);
+  InitProcessor();
+  InitSync();
+  EXPECT_TRUE(processor_.IsPreferred());
+  EXPECT_TRUE(processor_.IsConnected());
+
+  // Shutting down sync backend should disconnect but not disable the type.
+  UninitializeSync();
+  EXPECT_TRUE(processor_.IsPreferred());
+  EXPECT_FALSE(processor_.IsConnected());
+
+  // Brining the backend back should reconnect the type.
+  InitSync();
+  EXPECT_TRUE(processor_.IsPreferred());
+  EXPECT_TRUE(processor_.IsConnected());
+}
+
+// Test sync backend being restarted before processor connects.
+TEST_F(NonBlockingDataTypeControllerTest, RestartSyncBackendEarly) {
+  SetIsPreferred(true);
+
+  // Toggle sync off and on before the type processor is available.
+  InitSync();
+  EXPECT_FALSE(processor_.IsConnected());
+  UninitializeSync();
+  EXPECT_FALSE(processor_.IsConnected());
+  InitSync();
+  EXPECT_FALSE(processor_.IsConnected());
+
+  // Introduce the processor.
+  InitProcessor();
+  EXPECT_TRUE(processor_.IsConnected());
+}
+
+// Test pref toggling before the sync backend has connected.
+TEST_F(NonBlockingDataTypeControllerTest, TogglePreferenceWithoutBackend) {
+  SetIsPreferred(true);
+  InitProcessor();
+
+  // This should emit a disable signal.
+  SetIsPreferred(false);
+  EXPECT_FALSE(processor_.IsConnected());
+  EXPECT_FALSE(processor_.IsPreferred());
+
+  // This won't enable us, since we don't have a sync backend.
+  SetIsPreferred(true);
+  EXPECT_FALSE(processor_.IsConnected());
+  EXPECT_FALSE(processor_.IsPreferred());
+
+  // Only now do we start sending enable signals.
+  InitSync();
+  EXPECT_TRUE(processor_.IsConnected());
+  EXPECT_TRUE(processor_.IsPreferred());
+}
+
+}  // namespace
diff --git a/sync/internal_api/non_blocking_type_processor.cc b/sync/internal_api/non_blocking_type_processor.cc
index 8fd0d27..d426443 100644
--- a/sync/internal_api/non_blocking_type_processor.cc
+++ b/sync/internal_api/non_blocking_type_processor.cc
@@ -11,14 +11,22 @@
 namespace syncer {
 
 NonBlockingTypeProcessor::NonBlockingTypeProcessor(ModelType type)
-  : type_(type), enabled_(false), weak_ptr_factory_(this) {}
+  : type_(type),
+    is_preferred_(false),
+    is_connected_(false),
+    weak_ptr_factory_(this) {}
 
 NonBlockingTypeProcessor::~NonBlockingTypeProcessor() {
 }
 
-bool NonBlockingTypeProcessor::IsEnabled() const {
+bool NonBlockingTypeProcessor::IsPreferred() const {
   DCHECK(CalledOnValidThread());
-  return enabled_;
+  return is_preferred_;
+}
+
+bool NonBlockingTypeProcessor::IsConnected() const {
+  DCHECK(CalledOnValidThread());
+  return is_connected_;
 }
 
 ModelType NonBlockingTypeProcessor::GetModelType() const {
@@ -28,15 +36,19 @@ ModelType NonBlockingTypeProcessor::GetModelType() const {
 
 void NonBlockingTypeProcessor::Enable(SyncCoreProxy* core_proxy) {
   DCHECK(CalledOnValidThread());
-  core_proxy->ConnectTypeToCore(
-      GetModelType(),
-      AsWeakPtr());
+  is_preferred_ = true;
+  core_proxy->ConnectTypeToCore(GetModelType(), AsWeakPtr());
 }
 
 void NonBlockingTypeProcessor::Disable() {
   DCHECK(CalledOnValidThread());
-  enabled_ = false;
-  weak_ptr_factory_.InvalidateWeakPtrs();
+  is_preferred_ = false;
+  Disconnect();
+}
+
+void NonBlockingTypeProcessor::Disconnect() {
+  DCHECK(CalledOnValidThread());
+  is_connected_ = false;
   core_ = base::WeakPtr<NonBlockingTypeProcessorCore>();
   sync_thread_ = scoped_refptr<base::SequencedTaskRunner>();
 }
@@ -50,7 +62,7 @@ void NonBlockingTypeProcessor::OnConnect(
     base::WeakPtr<NonBlockingTypeProcessorCore> core,
     scoped_refptr<base::SequencedTaskRunner> sync_thread) {
   DCHECK(CalledOnValidThread());
-  enabled_ = true;
+  is_connected_ = true;
   core_ = core;
   sync_thread_ = sync_thread;
 }
diff --git a/sync/internal_api/public/non_blocking_type_processor.h b/sync/internal_api/public/non_blocking_type_processor.h
index 0198c27..3745088 100644
--- a/sync/internal_api/public/non_blocking_type_processor.h
+++ b/sync/internal_api/public/non_blocking_type_processor.h
@@ -24,8 +24,20 @@ class SYNC_EXPORT_PRIVATE NonBlockingTypeProcessor : base::NonThreadSafe {
   NonBlockingTypeProcessor(ModelType type);
   virtual ~NonBlockingTypeProcessor();
 
+  // Returns true if this object believes that sync is preferred for this type.
+  //
+  // By "preferred", we mean that a policy decision has been made that this
+  // type should be synced.  Most of the time this is controlled by a user
+  // clicking a checkbox on the settings page.
+  //
+  // The canonical preferred state is based on SyncPrefs on the UI thread.  At
+  // best, this value is stale and may lag behind the one set on the UI thread.
+  // Before this type has registered with the UI thread, it's mostly just an
+  // informed guess.
+  bool IsPreferred() const;
+
   // Returns true if the handshake with sync thread is complete.
-  bool IsEnabled() const;
+  bool IsConnected() const;
 
   // Returns the model type handled by this processor.
   ModelType GetModelType() const;
@@ -33,10 +45,14 @@ class SYNC_EXPORT_PRIVATE NonBlockingTypeProcessor : base::NonThreadSafe {
   // Starts the handshake with the sync thread.
   void Enable(SyncCoreProxy* core_proxy);
 
-  // Severs all ties to the sync thread.
+  // Severs all ties to the sync thread and may delete local sync state.
   // Another call to Enable() can be used to re-establish this connection.
   void Disable();
 
+  // Severs all ties to the sync thread.
+  // Another call to Enable() can be used to re-establish this connection.
+  void Disconnect();
+
   // Callback used to process the handshake response.
   void OnConnect(base::WeakPtr<NonBlockingTypeProcessorCore> core,
                  scoped_refptr<base::SequencedTaskRunner> sync_thread);
@@ -46,7 +62,14 @@ class SYNC_EXPORT_PRIVATE NonBlockingTypeProcessor : base::NonThreadSafe {
  private:
   ModelType type_;
   sync_pb::DataTypeProgressMarker progress_marker_;
-  bool enabled_;
+
+  // Whether or not sync is preferred for this type.  This is a cached copy of
+  // the canonical copy information on the UI thread.
+  bool is_preferred_;
+
+  // Whether or not this object has completed its initial handshake with the
+  // SyncCoreProxy.
+  bool is_connected_;
 
   base::WeakPtr<NonBlockingTypeProcessorCore> core_;
   scoped_refptr<base::SequencedTaskRunner> sync_thread_;
diff --git a/sync/internal_api/sync_core_proxy_impl_unittest.cc b/sync/internal_api/sync_core_proxy_impl_unittest.cc
index a3e228c..2e306ee 100644
--- a/sync/internal_api/sync_core_proxy_impl_unittest.cc
+++ b/sync/internal_api/sync_core_proxy_impl_unittest.cc
@@ -52,7 +52,7 @@ TEST_F(SyncCoreProxyImplTest, FailToConnect1) {
 
   base::RunLoop run_loop_;
   run_loop_.RunUntilIdle();
-  EXPECT_FALSE(themes_processor.IsEnabled());
+  EXPECT_FALSE(themes_processor.IsConnected());
 }
 
 // Try to connect a type to a SyncCore as it shuts down.
@@ -63,7 +63,7 @@ TEST_F(SyncCoreProxyImplTest, FailToConnect2) {
 
   base::RunLoop run_loop_;
   run_loop_.RunUntilIdle();
-  EXPECT_FALSE(themes_processor.IsEnabled());
+  EXPECT_FALSE(themes_processor.IsConnected());
 }
 
 // Tests the case where the type's processor shuts down first.
@@ -75,7 +75,7 @@ TEST_F(SyncCoreProxyImplTest, TypeDisconnectsFirst) {
   base::RunLoop run_loop_;
   run_loop_.RunUntilIdle();
 
-  EXPECT_TRUE(themes_processor->IsEnabled());
+  EXPECT_TRUE(themes_processor->IsConnected());
   themes_processor.reset();
 }
 
@@ -88,7 +88,7 @@ TEST_F(SyncCoreProxyImplTest, SyncDisconnectsFirst) {
   base::RunLoop run_loop_;
   run_loop_.RunUntilIdle();
 
-  EXPECT_TRUE(themes_processor->IsEnabled());
+  EXPECT_TRUE(themes_processor->IsConnected());
   DisableSync();
 }