[iOS] Correctly reload Sync Encryption settings screen on sync changes.

Sync Encryption screen now listens to sync changes and reloads itself
when necessary. This ensures modifications to the passphrase (done by
the Sync Encryption Passphrase screen) are reflected in the UI.

BUG=678609

Review-Url: https://codereview.chromium.org/2610403003
Cr-Commit-Position: refs/heads/master@{#441927}

ios/chrome/browser/ui/settings/sync_encryption_collection_view_controller.mm

@@ -6,6 +6,7 @@
 
 #import "base/ios/weak_nsobject.h"
 #import "base/mac/scoped_nsobject.h"
+#include "base/memory/ptr_util.h"
 #include "base/strings/sys_string_conversions.h"
 #include "components/browser_sync/profile_sync_service.h"
 #include "components/google/core/browser/google_util.h"
@@ -15,6 +16,7 @@
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #include "ios/chrome/browser/chrome_url_constants.h"
 #include "ios/chrome/browser/sync/ios_chrome_profile_sync_service_factory.h"
+#import "ios/chrome/browser/sync/sync_observer_bridge.h"
 #import "ios/chrome/browser/ui/collection_view/cells/MDCCollectionViewCell+Chrome.h"
 #import "ios/chrome/browser/ui/collection_view/cells/collection_view_footer_item.h"
 #import "ios/chrome/browser/ui/collection_view/cells/collection_view_item.h"
@@ -42,8 +44,10 @@ typedef NS_ENUM(NSInteger, ItemType) {
 
 }  // namespace
 
-@interface SyncEncryptionCollectionViewController () {
+@interface SyncEncryptionCollectionViewController ()<SyncObserverModelBridge> {
   ios::ChromeBrowserState* _browserState;
+  std::unique_ptr<SyncObserverBridge> _syncObserver;
+  BOOL _isUsingSecondaryPassphrase;
 }
 // Returns an account item.
 - (CollectionViewItem*)accountItem;
@@ -63,6 +67,11 @@ typedef NS_ENUM(NSInteger, ItemType) {
   if (self) {
     self.title = l10n_util::GetNSString(IDS_IOS_SYNC_ENCRYPTION_TITLE);
     _browserState = browserState;
+    browser_sync::ProfileSyncService* syncService =
+        IOSChromeProfileSyncServiceFactory::GetForBrowserState(_browserState);
+    _isUsingSecondaryPassphrase = syncService->IsEngineInitialized() &&
+                                  syncService->IsUsingSecondaryPassphrase();
+    _syncObserver = base::MakeUnique<SyncObserverBridge>(self, syncService);
     [self loadModel];
   }
   return self;
@@ -80,9 +89,7 @@ typedef NS_ENUM(NSInteger, ItemType) {
   [model addItem:[self passphraseItem]
       toSectionWithIdentifier:SectionIdentifierEncryption];
 
-  browser_sync::ProfileSyncService* service =
-      IOSChromeProfileSyncServiceFactory::GetForBrowserState(_browserState);
-  if (service->IsEngineInitialized() && service->IsUsingSecondaryPassphrase()) {
+  if (_isUsingSecondaryPassphrase) {
     [model addSectionWithIdentifier:SectionIdentifierFooter];
     [model addItem:[self footerItem]
         toSectionWithIdentifier:SectionIdentifierFooter];
@@ -93,35 +100,20 @@ typedef NS_ENUM(NSInteger, ItemType) {
 
 - (CollectionViewItem*)accountItem {
   DCHECK(browser_sync::ProfileSyncService::IsSyncAllowedByFlag());
-  BOOL checkedAndEnabled = YES;
-  browser_sync::ProfileSyncService* service =
-      IOSChromeProfileSyncServiceFactory::GetForBrowserState(_browserState);
-  if (service->IsEngineInitialized() && service->IsUsingSecondaryPassphrase()) {
-    checkedAndEnabled = NO;
-  }
   NSString* text = l10n_util::GetNSString(IDS_SYNC_BASIC_ENCRYPTION_DATA);
   return [self itemWithType:ItemTypeAccount
                        text:text
-                    checked:checkedAndEnabled
-                    enabled:checkedAndEnabled];
+                    checked:!_isUsingSecondaryPassphrase
+                    enabled:!_isUsingSecondaryPassphrase];
 }
 
 - (CollectionViewItem*)passphraseItem {
   DCHECK(browser_sync::ProfileSyncService::IsSyncAllowedByFlag());
-  BOOL checked = NO;
-  BOOL enabled = NO;
-  browser_sync::ProfileSyncService* service =
-      IOSChromeProfileSyncServiceFactory::GetForBrowserState(_browserState);
-  if (service->IsEngineInitialized() && service->IsUsingSecondaryPassphrase()) {
-    checked = YES;
-  } else {
-    enabled = YES;
-  }
   NSString* text = l10n_util::GetNSString(IDS_SYNC_FULL_ENCRYPTION_DATA);
   return [self itemWithType:ItemTypePassphrase
                        text:text
-                    checked:checked
-                    enabled:enabled];
+                    checked:_isUsingSecondaryPassphrase
+                    enabled:!_isUsingSecondaryPassphrase];
 }
 
 - (CollectionViewItem*)footerItem {
@@ -213,6 +205,19 @@ typedef NS_ENUM(NSInteger, ItemType) {
   }
 }
 
+#pragma mark SyncObserverModelBridge
+
+- (void)onSyncStateChanged {
+  browser_sync::ProfileSyncService* service =
+      IOSChromeProfileSyncServiceFactory::GetForBrowserState(_browserState);
+  BOOL isNowUsingSecondaryPassphrase =
+      service->IsEngineInitialized() && service->IsUsingSecondaryPassphrase();
+  if (_isUsingSecondaryPassphrase != isNowUsingSecondaryPassphrase) {
+    _isUsingSecondaryPassphrase = isNowUsingSecondaryPassphrase;
+    [self reloadData];
+  }
+}
+
 #pragma mark - Private methods
 
 - (CollectionViewItem*)itemWithType:(NSInteger)type