[iOS] Add hover pointer support for User signin

iOS 13.4 introduces new APIs for mouse cursor support on iPad.

Buttons should react to pointer hover. This CL enables the default
hover effect in the user signin screen.

Test: iPad only. Enable pointer support flag. Ensure buttons respond to pointer in user signin screen.
Bug: 1073961
Change-Id: Ied2f4a4185e5c0346d49059f8c46d6c363e0eda9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2168642Reviewed-by: Jérôme Lebel <jlebel@chromium.org>
Commit-Queue: edchin <edchin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#763446}

ios/chrome/browser/ui/authentication/signin/user_signin/BUILD.gn

@@ -19,6 +19,7 @@ source_set("user_signin") {
     "user_signin_view_controller.mm",
   ]
   deps = [
+    "//base",
     "//components/consent_auditor",
     "//components/sync/base",
     "//components/unified_consent",
@@ -26,6 +27,7 @@ source_set("user_signin") {
     "//ios/chrome/browser/main:public",
     "//ios/chrome/browser/signin",
     "//ios/chrome/browser/sync",
+    "//ios/chrome/browser/ui:feature_flags",
     "//ios/chrome/browser/ui/authentication",
     "//ios/chrome/browser/ui/authentication/signin:signin_headers",
     "//ios/chrome/browser/ui/authentication/signin:signin_protected",

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

@@ -4,9 +4,11 @@
 
 #import "ios/chrome/browser/ui/authentication/signin/user_signin/user_signin_view_controller.h"
 
+#include "base/feature_list.h"
 #import "base/logging.h"
 #import "ios/chrome/browser/ui/authentication/signin/signin_constants.h"
 #import "ios/chrome/browser/ui/authentication/signin/user_signin/gradient_view.h"
+#include "ios/chrome/browser/ui/ui_feature_flags.h"
 #import "ios/chrome/browser/ui/util/rtl_geometry.h"
 #import "ios/chrome/browser/ui/util/uikit_ui_util.h"
 #import "ios/chrome/common/ui/colors/UIColor+cr_semantic_colors.h"
@@ -406,6 +408,13 @@ enum AuthenticationButtonType {
   DCHECK(self.unifiedConsentViewController);
   self.confirmationButton = [[UIButton alloc] init];
   self.confirmationButton.accessibilityIdentifier = @"ic_close";
+#if defined(__IPHONE_13_4)
+  if (@available(iOS 13.4, *)) {
+    if (base::FeatureList::IsEnabled(kPointerSupport)) {
+      self.confirmationButton.pointerInteractionEnabled = YES;
+    }
+  }
+#endif  // defined(__IPHONE_13_4)
 
   [self addSubviewWithButton:self.confirmationButton];
   // Note that the button style will depend on the user sign-in state.
@@ -426,6 +435,13 @@ enum AuthenticationButtonType {
   [self.skipSigninButton addTarget:self
                             action:@selector(onSkipSigninButtonPressed:)
                   forControlEvents:UIControlEventTouchUpInside];
+#if defined(__IPHONE_13_4)
+  if (@available(iOS 13.4, *)) {
+    if (base::FeatureList::IsEnabled(kPointerSupport)) {
+      self.skipSigninButton.pointerInteractionEnabled = YES;
+    }
+  }
+#endif  // defined(__IPHONE_13_4)
 }
 
 // Sets up button properties and adds it to view.