sk_sp: fix contravariant constructors

include/core/SkRefCnt.h

Index: include/core/SkRefCnt.h
diff --git a/include/core/SkRefCnt.h b/include/core/SkRefCnt.h
index 9e8f3be61c33456de32384af7a25f84326d30989..9b05ad49698cb2b6ea15f84e670b24492d0eff9e 100644
--- a/include/core/SkRefCnt.h
+++ b/include/core/SkRefCnt.h
@@ -250,7 +250,7 @@ public:
      */
     sk_sp(const sk_sp<T>& that) : fPtr(SkSafeRef(that.get())) {}
     template <typename U,
-              typename = skstd::enable_if_t<skstd::is_convertible<U, T>::value>>
+              typename = skstd::enable_if_t<skstd::is_convertible<U*, T*>::value>>
     sk_sp(const sk_sp<U>& that) : fPtr(SkSafeRef(that.get())) {}
 
     /**
@@ -260,7 +260,7 @@ public:
      */
     sk_sp(sk_sp<T>&& that) : fPtr(that.release()) {}
     template <typename U,
-              typename = skstd::enable_if_t<skstd::is_convertible<U, T>::value>>
+              typename = skstd::enable_if_t<skstd::is_convertible<U*, T*>::value>>
     sk_sp(sk_sp<U>&& that) : fPtr(that.release()) {}
 
     /**
@@ -288,7 +288,7 @@ public:
         return *this;
     }
     template <typename U,
-              typename = skstd::enable_if_t<skstd::is_convertible<U, T>::value>>
+              typename = skstd::enable_if_t<skstd::is_convertible<U*, T*>::value>>
     sk_sp<T>& operator=(const sk_sp<U>& that) {
         this->reset(SkSafeRef(that.get()));
         return *this;
@@ -304,7 +304,7 @@ public:
         return *this;
     }
     template <typename U,
-              typename = skstd::enable_if_t<skstd::is_convertible<U, T>::value>>
+              typename = skstd::enable_if_t<skstd::is_convertible<U*, T*>::value>>
     sk_sp<T>& operator=(sk_sp<U>&& that) {
         this->reset(that.release());
         return *this;