[iOS] Fixing skip button in sign-in

Adding adding content edge insets for the skip button in the user
sign-in coordinator.
Updating the skip button title, to always be in upper case, to match
the old implementation (MDCButton seems to always have upper case
title).

Before:
https://drive.google.com/open?id=1a1worTgClUtfs3p3YUwp45vH3-DhCflJ
After:
https://drive.google.com/open?id=19MrZ6a-lP1LBUWonredKKY3zxM4SbsGQ

Bug: 971989
Change-Id: I0eddfc2d855413926e794af1713aedc916a82656
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2130549
Auto-Submit: Jérôme Lebel <jlebel@chromium.org>
Commit-Queue: Nohemi Fernandez <fernandex@chromium.org>
Reviewed-by: Nohemi Fernandez <fernandex@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755290}

ios/chrome/browser/ui/authentication/signin/user_signin/user_signin_view_controller.mm

@@ -280,12 +280,15 @@ enum AuthenticationButtonType {
   DCHECK(self.unifiedConsentViewController);
   self.skipSigninButton = [[UIButton alloc] init];
   [self addSubviewWithButton:self.skipSigninButton];
-  [self.skipSigninButton setTitle:self.skipSigninButtonTitle
+  [self.skipSigninButton setTitle:self.skipSigninButtonTitle.uppercaseString
                          forState:UIControlStateNormal];
   [self setSkipSigninStylingWithButton:self.skipSigninButton];
   [self.skipSigninButton addTarget:self
                             action:@selector(onSkipSigninButtonPressed:)
                   forControlEvents:UIControlEventTouchUpInside];
+  self.skipSigninButton.contentEdgeInsets =
+      UIEdgeInsetsMake(kButtonTitleContentInset, kButtonTitleContentInset,
+                       kButtonTitleContentInset, kButtonTitleContentInset);
 }
 
 // Sets up button properties and adds it to view.