[ObjC ARC] Converts ios/public/provider/chrome/browser/signin:signin to ARC.

ios/public/provider/chrome/browser/signin/chrome_identity_interaction_manager.mm

Index: ios/public/provider/chrome/browser/signin/chrome_identity_interaction_manager.mm
diff --git a/ios/public/provider/chrome/browser/signin/chrome_identity_interaction_manager.mm b/ios/public/provider/chrome/browser/signin/chrome_identity_interaction_manager.mm
index 6e5b223dd24e65a4fdb8970a510764888b01f090..4be67232e786c34ff50fe4ade806fb4d498fc13e 100644
--- a/ios/public/provider/chrome/browser/signin/chrome_identity_interaction_manager.mm
+++ b/ios/public/provider/chrome/browser/signin/chrome_identity_interaction_manager.mm
@@ -4,23 +4,14 @@
 
 #import "ios/public/provider/chrome/browser/signin/chrome_identity_interaction_manager.h"
 
-#import "base/ios/weak_nsobject.h"
 #include "base/logging.h"
 
-@interface ChromeIdentityInteractionManager () {
-  base::WeakNSProtocol<id<ChromeIdentityInteractionManagerDelegate>> _delegate;
-}
-@end
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
 
 @implementation ChromeIdentityInteractionManager
-
-- (id<ChromeIdentityInteractionManagerDelegate>)delegate {
-  return _delegate;
-}
-
-- (void)setDelegate:(id<ChromeIdentityInteractionManagerDelegate>)delegate {
-  _delegate.reset(delegate);
-}
+@synthesize delegate = _delegate;
 
 - (BOOL)isCanceling {
   return NO;