[iOS] Don't show the NTP avatar when signed out

This CL hides the NTP avatar when the user isn't signed in.

Fixed: 1115654
Change-Id: Idfcdadddbfb2ccd81000833d561aca46ac8074cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2375247
Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Sergio Collazos <sczs@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#801693}

ios/chrome/browser/ui/content_suggestions/content_suggestions_header_view_controller.mm

@@ -706,6 +706,7 @@ const NSString* kScribbleFakeboxElementId = @"fakebox";
 #pragma mark - UserAccountImageUpdateDelegate
 
 - (void)updateAccountImage:(UIImage*)image {
+  self.identityDiscButton.hidden = !image;
   [self.identityDiscButton setImage:image forState:UIControlStateNormal];
   self.identityDiscButton.imageView.layer.cornerRadius = image.size.width / 2;
   self.identityDiscButton.imageView.layer.masksToBounds = YES;

ios/chrome/browser/ui/content_suggestions/ntp_home_mediator.mm

@@ -681,13 +681,14 @@ const char kNTPHelpURL[] =
       identityService->GetAvatarForIdentity(identity, nil);
     }
   } else {
-    // User is not signed in, show default avatar.
-    image = [self defaultAvatar];
+    // User is not signed in, don't show any avatar.
+    image = nil;
   }
   // TODO(crbug.com/965962): Use ResizedAvatarCache when it accepts the
   // specification of different image sizes.
   CGFloat dimension = ntp_home::kIdentityAvatarDimension;
-  if (image.size.width != dimension || image.size.height != dimension) {
+  if (image &&
+      (image.size.width != dimension || image.size.height != dimension)) {
     image = ResizeImage(image, CGSizeMake(dimension, dimension),
                         ProjectionMode::kAspectFit);
   }