sk_sp: remove explicit operator bool()

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 277 matching lines @@
         this->reset(that.release());
         return *this;
     }
 
     bool operator==(std::nullptr_t) const { return this->get() == nullptr; }
     bool operator!=(std::nullptr_t) const { return this->get() != nullptr; }
 
     bool operator==(const sk_sp<T>& that) const { return this->get() == that.get(); }
     bool operator!=(const sk_sp<T>& that) const { return this->get() != that.get(); }
 
-    explicit operator bool() const { return this->get() != nullptr; }
+    // MSVC 2013 does not work correctly with explicit operator bool.
+    // https://chromium-cpp.appspot.com/#core-blacklist
+    //explicit operator bool() const { return this->get() != nullptr; }
+
+    bool operator!() const { return this->get() == nullptr; }
 
     T* get() const { return fPtr; }
     T* operator->() const { return fPtr; }
 
     /**
      *  Adopt the new bare pointer, and call unref() on any previously held object (if not null).
      *  No call to ref() will be made.
      */
     void reset(T* ptr = nullptr) {
         if (fPtr != ptr) {
@@ skipping 11 matching lines @@
         T* ptr = fPtr;
         fPtr = nullptr;
         return ptr;
     }
 
 private:
     T*  fPtr;
 };
 
 #endif