Add an explicit bool conversion to scoped_refptr<T>.

base/memory/ref_counted.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_MEMORY_REF_COUNTED_H_
 #define BASE_MEMORY_REF_COUNTED_H_
 
 #include <cassert>
 #include <iosfwd>
 
@@ skipping 285 matching lines @@
   }
 
   T* get() const { return ptr_; }
 
 #if !defined(DISABLE_SCOPED_REFPTR_CONVERSION_OPERATOR)
   // Allow scoped_refptr<C> to be used in boolean expression
   // and comparison operations.
   operator T*() const { return ptr_; }
 #endif
 
+  explicit operator bool() const { return ptr_ != nullptr; }
+
   T& operator*() const {
-    assert(ptr_ != NULL);
+    assert(ptr_ != nullptr);
     return *ptr_;
   }
 
   T* operator->() const {
-    assert(ptr_ != NULL);
+    assert(ptr_ != nullptr);
     return ptr_;
   }
 
   scoped_refptr<T>& operator=(T* p) {
     // AddRef first so that self assignment should work
     if (p)
       p->AddRef();
     T* old_ptr = ptr_;
     ptr_ = p;
     if (old_ptr)
@@ skipping 70 matching lines @@
   return !operator==(lhs, rhs);
 }
 
 template <typename T>
 std::ostream& operator<<(std::ostream& out, const scoped_refptr<T>& p) {
   return out << p.get();
 }
 #endif  // defined(DISABLE_SCOPED_REFPTR_CONVERSION_OPERATOR)
 
 #endif  // BASE_MEMORY_REF_COUNTED_H_