Add -[CWVSyncController shutDown]

CWVSyncController needs a way to unobserve signin::IdentityManager
before its associated CWVWebViewConfiguration destroys its
WebViewBrowserState. This avoids a DCHECK in the IdentityManager's
observer list.

Change-Id: I1a0d15bc4bc57a3cf1dd7fbc5a38bdb0adefad0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2067472Reviewed-by: Hiroshi Ichikawa <ichikawa@chromium.org>
Commit-Queue: John Wu <jzw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#743390}

ios/web_view/internal/cwv_web_view_configuration.mm

@@ -205,6 +205,9 @@ CWVWebViewConfiguration* gIncognitoConfiguration = nil;
   for (CWVWebView* webView in _webViews) {
     [webView shutDown];
   }
+#if BUILDFLAG(IOS_WEB_VIEW_ENABLE_SYNC)
+  [_syncController shutDown];
+#endif  // BUILDFLAG(IOS_WEB_VIEW_ENABLE_SYNC)
   _browserState.reset();
 }
 

ios/web_view/internal/sync/cwv_sync_controller.mm

@@ -290,6 +290,12 @@ __weak id<CWVSyncControllerDataSource> gSyncDataSource;
 
 #pragma mark - Internal Methods
 
+- (void)shutDown {
+  _syncService->RemoveObserver(_observer.get());
+  _identityManager->RemoveObserver(_observer.get());
+  _signinErrorController->RemoveObserver(_observer.get());
+}
+
 // Create and return a callback that is used to notify when a clean up task
 // completes.
 - (base::OnceClosure)pendingCleanupTaskCallback {

ios/web_view/internal/sync/cwv_sync_controller_internal.h

@@ -41,6 +41,10 @@ class SigninErrorController;
              passwordStore:(password_manager::PasswordStore*)passwordStore
     NS_DESIGNATED_INITIALIZER;
 
+// Called by the associated CWVWebViewConfiguration in order to shut
+// down cleanly. See CWVWebViewConfiguration's |shutDown| method for more info.
+- (void)shutDown;
+
 @end
 
 NS_ASSUME_NONNULL_END