[ios] Dismiss container banner when manager changes.

When the InfobarManager will change dismiss the current Banner being
presented in order to avoid the banner to be dismissed when the manager
has already changed leading to some crashes.

Bug: 1054024
Change-Id: Ia85b09b0bff300887a896b1a1c0e5887735edaa6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2248859
Commit-Queue: Sergio Collazos <sczs@chromium.org>
Auto-Submit: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Chris Lu <thegreenfrog@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779198}

ios/chrome/browser/ui/infobars/infobar_container_coordinator.mm

@@ -243,6 +243,9 @@
 }
 
 - (void)infobarManagerWillChange {
+  if (IsInfobarUIRebootEnabled()) {
+    [self dismissInfobarBannerAnimated:NO completion:nil];
+  }
   self.infobarCoordinators = [NSMutableArray array];
   self.infobarCoordinatorsToPresent = [NSMutableArray array];
 }