sk_sp: remove explicit operator bool()

include/core/SkRefCnt.h

Index: include/core/SkRefCnt.h
diff --git a/include/core/SkRefCnt.h b/include/core/SkRefCnt.h
index 43251d0788c2e6a992965da626729da035d9e165..fea146d35f6536af78a11bcb87b3f63191b12bbb 100644
--- a/include/core/SkRefCnt.h
+++ b/include/core/SkRefCnt.h
@@ -295,7 +295,11 @@ public:
     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; }