[iOS] Implementing swipe to dismiss the sign-in view controller

In ChromeSigninViewController, when a swipe to dismiss is done by the
user, the secondary button (Cancel) action is triggered.
The swipe to dismiss does the exact same behavior than the Cancel button.
Swipe to dismiss is only enabled for UnityConsent flag enabled.

Bug: 987232
Change-Id: I3dc6f41a49652e3a2c4482628f26e1de5621ab47
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1715292
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682203}

ios/chrome/browser/ui/authentication/chrome_signin_view_controller.h

@@ -69,7 +69,10 @@ using TimerGeneratorBlock = std::unique_ptr<base::OneShotTimer> (^)();
 @end
 
 // ChromeSigninViewController is a view controller that handles all the
-// sign-in UI flow.
+// sign-in UI flow. To support the swipe to dismiss feature, the init method of
+// this class uses the presentation controller. Therefore the presentation style
+// cannot be changed after the init. The style is set to
+// UIModalPresentationFormSheet by the init method.
 @interface ChromeSigninViewController
     : UIViewController<SigninConfirmationViewControllerDelegate>
 

ios/chrome/browser/ui/authentication/chrome_signin_view_controller.mm

@@ -137,11 +137,12 @@ enum AuthenticationState {
 
 }  // namespace
 
-@interface ChromeSigninViewController ()<
+@interface ChromeSigninViewController () <
     ChromeIdentityInteractionManagerDelegate,
     ChromeIdentityServiceObserver,
     MDCActivityIndicatorDelegate,
     SigninAccountSelectorViewControllerDelegate,
+    UIAdaptivePresentationControllerDelegate,
     UnifiedConsentCoordinatorDelegate>
 @property(nonatomic, strong) ChromeIdentity* selectedIdentity;
 @end
@@ -215,6 +216,9 @@ enum AuthenticationState {
     _identityServiceObserver.reset(
         new ChromeIdentityServiceObserverBridge(self));
     _currentState = NULL_STATE;
+
+    self.modalPresentationStyle = UIModalPresentationFormSheet;
+    self.presentationController.delegate = self;
   }
   return self;
 }
@@ -507,6 +511,18 @@ enum AuthenticationState {
   ];
 }
 
+#pragma mark - UIAdaptivePresentationController
+
+- (BOOL)presentationControllerShouldDismiss:
+    (UIPresentationController*)presentationController {
+  return _unifiedConsentEnabled;
+}
+
+- (void)presentationControllerDidDismiss:
+    (UIPresentationController*)presentationController {
+  [self onSecondaryButtonPressed:self];
+}
+
 #pragma mark - Accessibility
 
 - (BOOL)accessibilityPerformEscape {

ios/chrome/browser/ui/signin_interaction/signin_interaction_controller.mm

@@ -265,11 +265,7 @@
                                                    promoAction:promoAction_
                                                 signInIdentity:signInIdentity
                                                     dispatcher:self.dispatcher];
-  [signinViewController_ setDelegate:self];
-  [signinViewController_
-      setModalPresentationStyle:UIModalPresentationFormSheet];
-  [signinViewController_
-      setModalTransitionStyle:UIModalTransitionStyleCoverVertical];
+  signinViewController_.delegate = self;
   signInIdentity_ = signInIdentity;
   identityAdded_ = identityAdded;