[iOS] Fixing issue when rotating device while signing in

"Reach bottom" notification from the user consent view should be ignored
when the sign-in is started. This can happens when the device is
rotated (with the screen height changing).

Bug: 995987
Change-Id: Iead0dc2b6a31833ae169a12c30f984a3a6327026
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1765671Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691991}

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

@@ -1306,7 +1306,12 @@ enum AuthenticationState {
 - (void)unifiedConsentCoordinatorDidReachBottom:
     (UnifiedConsentCoordinator*)coordinator {
   DCHECK_EQ(_unifiedConsentCoordinator, coordinator);
-  DCHECK_EQ(IDENTITY_PICKER_STATE, _currentState);
+  if (_currentState != IDENTITY_PICKER_STATE) {
+    // While signing in with rotation, the unified consent view controller,
+    // might trigger "reach bottom" notification. Those notification should
+    // be ignored if the sign-in already started.
+    return;
+  }
   [self didReachBottom];
 }