sk_sp for gpu.

include/core/SkRefCnt.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkRefCnt_DEFINED
 #define SkRefCnt_DEFINED
 
@@ skipping 246 matching lines @@
  *  This can be used for classes inheriting from SkRefCnt, but it also works for other
  *  classes that match the interface, but have different internal choices: e.g. the hosted class
  *  may have its ref/unref be thread-safe, but that is not assumed/imposed by sk_sp.
  */
 template <typename T> class sk_sp {
     /** Supports safe bool idiom. Obsolete with explicit operator bool. */
     using unspecified_bool_type = T* sk_sp::*;
 public:
     using element_type = T;
 
-    sk_sp() : fPtr(nullptr) {}
-    sk_sp(std::nullptr_t) : fPtr(nullptr) {}
+    constexpr sk_sp() : fPtr(nullptr) {}
+    constexpr sk_sp(std::nullptr_t) : fPtr(nullptr) {}
 
     /**
      *  Shares the underlying object by calling ref(), so that both the argument and the newly
      *  created sk_sp both have a reference to it.
      */
     sk_sp(const sk_sp<T>& that) : fPtr(SkSafeRef(that.get())) {}
     template <typename U, typename = skstd::enable_if_t<std::is_convertible<U*, T*>::value>>
     sk_sp(const sk_sp<U>& that) : fPtr(SkSafeRef(that.get())) {}
 
     /**
@@ skipping 181 matching lines @@
  *
  *  This function may be helpful while we convert callers from ptr-based to sk_sp-based parameters.
  */
 template <typename T> sk_sp<T> sk_ref_sp(T* obj) {
     return sk_sp<T>(SkSafeRef(obj));
 }
 
 #endif
 
 #endif