[sync/android] Make decoupled_from_master_sync a one-shot device pref

Before this CL, sign-out would clear the pref representing whether Sync
should be decoupled from the Android master sync toggle. This CL
removes the clean-up logic and also makes sure that the pref is set
whenever ProfileSyncService detects there's no syncing account (either
on browser startup, or after sign-out). Indeed, by the time the
DecoupleSyncFromAndroidMasterSync feature is enabled, only users who
were already syncing but had the master toggle disabled should remain
in the coupled state.

Bug: 1105795
Change-Id: If5e36080159150fe976885b469696103df890ed4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2539202
Commit-Queue: Victor Vianna <victorvianna@google.com>
Reviewed-by: Marc Treib <treib@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827887}

components/sync/base/pref_names.cc

@@ -108,6 +108,7 @@ const char kLocalSyncBackendDir[] = "sync.local_sync_backend_dir";
 #if defined(OS_ANDROID)
 // Stores whether sync should no longer respect the state of master toggle for
 // this user.
+// TODO(crbug.com/1107904): Clean pref when the decoupling logic is removed.
 const char kSyncDecoupledFromAndroidMasterSync[] =
     "sync.decoupled_from_master_sync";
 #endif  // defined(OS_ANDROID)

components/sync/base/sync_prefs.cc

@@ -226,9 +226,6 @@ void SyncPrefs::ClearLocalSyncTransportData() {
   pref_service_->ClearPref(prefs::kSyncCacheGuid);
   pref_service_->ClearPref(prefs::kSyncBirthday);
   pref_service_->ClearPref(prefs::kSyncBagOfChips);
-#if defined(OS_ANDROID)
-  pref_service_->ClearPref(prefs::kSyncDecoupledFromAndroidMasterSync);
-#endif  // defined(OS_ANDROID)
 
   // No need to clear kManaged, kEnableLocalSyncBackend or kLocalSyncBackendDir,
   // since they're never actually set as user preferences.

components/sync/base/sync_prefs.h

@@ -166,7 +166,8 @@ class SyncPrefs : public CryptoSyncPrefs,
 
 #if defined(OS_ANDROID)
   // Sets a boolean pref representing that Sync should no longer respect whether
-  // Android master sync is enabled/disabled.
+  // Android master sync is enabled/disabled. It is set per-device and never
+  // gets cleared.
   void SetDecoupledFromAndroidMasterSync();
 
   // Gets the value for the boolean pref representing whether Sync should no

components/sync/driver/profile_sync_service.cc

@@ -334,6 +334,16 @@ void ProfileSyncService::Initialize() {
   RecordSyncInitialState(GetDisableReasons(),
                          user_settings_->IsFirstSetupComplete());
 
+#if defined(OS_ANDROID)
+  // If Sync was turned on after the feature toggle was enabled, it should be in
+  // the decoupled state.
+  if (!IsAuthenticatedAccountPrimary() &&
+      base::FeatureList::IsEnabled(
+          switches::kDecoupleSyncFromAndroidMasterSync)) {
+    sync_prefs_.SetDecoupledFromAndroidMasterSync();
+  }
+#endif  // defined(OS_ANDROID)
+
   // Auto-start means the first time the profile starts up, sync should start up
   // immediately. Since IsSyncRequested() is false by default and nobody else
   // will set it, we need to set it here.
@@ -386,6 +396,17 @@ WeakHandle<JsEventHandler> ProfileSyncService::GetJsEventHandler() {
 void ProfileSyncService::AccountStateChanged() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
+#if defined(OS_ANDROID)
+  // Once the feature toggle is enabled, Sync and master sync should only remain
+  // coupled if the former stays enabled and the latter disabled. Upon sign-out
+  // set the pref so they are decoupled on the next time Sync is turned on.
+  if (!IsAuthenticatedAccountPrimary() &&
+      base::FeatureList::IsEnabled(
+          switches::kDecoupleSyncFromAndroidMasterSync)) {
+    sync_prefs_.SetDecoupledFromAndroidMasterSync();
+  }
+#endif  // defined(OS_ANDROID)
+
   if (!IsSignedIn()) {
     // The account was signed out, so shut down.
     sync_disabled_by_admin_ = false;

components/sync/driver/profile_sync_service.h

@@ -209,7 +209,8 @@ class ProfileSyncService : public SyncService,
 
 #if defined(OS_ANDROID)
   // Persists the fact that sync should no longer respect whether Android master
-  // sync is enabled. Only called on Android.
+  // sync is enabled. This will be respected for the current syncing account
+  // (if one exists) and any future ones. Only called on Android.
   void SetDecoupledFromAndroidMasterSync();
 
   // Gets the persisted information of whether sync should no longer respect

components/sync/driver/profile_sync_service_unittest.cc

@@ -17,6 +17,7 @@
 #include "base/test/task_environment.h"
 #include "base/time/time.h"
 #include "base/values.h"
+#include "build/build_config.h"
 #include "components/policy/core/common/policy_service_impl.h"
 #include "components/prefs/testing_pref_service.h"
 #include "components/signin/public/identity_manager/account_info.h"
@@ -1390,6 +1391,44 @@ TEST_F(ProfileSyncServiceTest, ShouldPopulateAccountIdCachedInPrefs) {
   EXPECT_EQ(signin::GetTestGaiaIdForEmail(kTestUser), sync_prefs.GetGaiaId());
 }
 
+#if defined(OS_ANDROID)
+TEST_F(ProfileSyncServiceTest, DecoupleFromMasterSyncIfInitializedSignedOut) {
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndEnableFeature(
+      switches::kDecoupleSyncFromAndroidMasterSync);
+
+  SyncPrefs sync_prefs(prefs());
+  CreateService(ProfileSyncService::MANUAL_START);
+  ASSERT_FALSE(sync_prefs.GetDecoupledFromAndroidMasterSync());
+
+  service()->Initialize();
+  EXPECT_TRUE(sync_prefs.GetDecoupledFromAndroidMasterSync());
+}
+
+TEST_F(ProfileSyncServiceTest, DecoupleFromMasterSyncIfSignsOut) {
+  base::test::ScopedFeatureList feature_list;
+  feature_list.InitAndEnableFeature(
+      switches::kDecoupleSyncFromAndroidMasterSync);
+
+  SyncPrefs sync_prefs(prefs());
+  SignIn();
+  CreateService(ProfileSyncService::MANUAL_START);
+  InitializeForNthSync();
+  ASSERT_FALSE(sync_prefs.GetDecoupledFromAndroidMasterSync());
+
+  // Sign-out.
+  auto* account_mutator = identity_manager()->GetPrimaryAccountMutator();
+  DCHECK(account_mutator) << "Account mutator should only be null on ChromeOS.";
+  account_mutator->ClearPrimaryAccount(
+      signin::PrimaryAccountMutator::ClearAccountsAction::kDefault,
+      signin_metrics::SIGNOUT_TEST,
+      signin_metrics::SignoutDelete::IGNORE_METRIC);
+  // Wait for ProfileSyncService to be notified.
+  base::RunLoop().RunUntilIdle();
+  EXPECT_TRUE(sync_prefs.GetDecoupledFromAndroidMasterSync());
+}
+#endif  // defined(OS_ANDROID)
+
 TEST_F(ProfileSyncServiceTest,
        ShouldNotPopulateAccountIdCachedInPrefsWithLocalSync) {
   SyncPrefs sync_prefs(prefs());