[iOS] Add completion parameter to ChromeIdentityService cancel API.

In response to b/149180809 an additional parameter was added to the
cancel add account flow. Update service accordingly.

Bug: 1078815
Change-Id: I34bd4aa9a68bd949ce78d366afcee0f7b3fc423f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2207158
Auto-Submit: Nohemi Fernandez <fernandex@chromium.org>
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Reviewed-by: Jérôme Lebel <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770049}

ios/public/provider/chrome/browser/signin/chrome_identity_interaction_manager.h

@@ -77,7 +77,9 @@ typedef void (^SigninCompletionCallback)(ChromeIdentity* identity,
 
 // Cancels and dismisses any currently active operation.
 // * |animated| represents whether the UI should be dismissed with an animation.
-- (void)cancelAddAccountWithAnimation:(BOOL)animated;
+// * |completion| will be called once the operation has finished.
+- (void)cancelAddAccountWithAnimation:(BOOL)animated
+                           completion:(void (^)(void))completion;
 
 @end
 

ios/public/provider/chrome/browser/signin/chrome_identity_interaction_manager.mm

@@ -46,7 +46,8 @@
   NOTREACHED() << "Subclasses must override this";
 }
 
-- (void)cancelAddAccountWithAnimation:(BOOL)animated {
+- (void)cancelAddAccountWithAnimation:(BOOL)animated
+                           completion:(void (^)(void))completion {
   NOTREACHED() << "Subclasses must override this";
 }