Allow nullptr to be converted to JavaRef subclasses.

base/android/scoped_java_ref.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_ANDROID_SCOPED_JAVA_REF_H_
 #define BASE_ANDROID_SCOPED_JAVA_REF_H_
 
 #include <jni.h>
 #include <stddef.h>
 
@@ skipping 130 matching lines @@
 // thread, objects of this class must be created, used, and destroyed, on a
 // single thread.
 // Therefore, this class should only be used as a stack-based object and from a
 // single thread. If you wish to have the reference outlive the current
 // callstack (e.g. as a class member) or you wish to pass it across threads,
 // use a ScopedJavaGlobalRef instead.
 template<typename T>
 class ScopedJavaLocalRef : public JavaRef<T> {
  public:
   ScopedJavaLocalRef() : env_(nullptr) {}
+  ScopedJavaLocalRef(std::nullptr_t) : env_(nullptr) {}
 
   // Non-explicit copy constructor, to allow ScopedJavaLocalRef to be returned
   // by value as this is the normal usage pattern.
   ScopedJavaLocalRef(const ScopedJavaLocalRef<T>& other)
       : env_(other.env_) {
     this->SetNewLocalRef(env_, other.obj());
   }
 
   ScopedJavaLocalRef(ScopedJavaLocalRef<T>&& other) : env_(other.env_) {
     this->swap(other);
@@ skipping 70 matching lines @@
 };
 
 // Holds a global reference to a Java object. The global reference is scoped
 // to the lifetime of this object. This class does not hold onto any JNIEnv*
 // passed to it, hence it is safe to use across threads (within the constraints
 // imposed by the underlying Java object that it references).
 template<typename T>
 class ScopedJavaGlobalRef : public JavaRef<T> {
  public:
   ScopedJavaGlobalRef() {}
+  ScopedJavaGlobalRef(std::nullptr_t) {}
 
   ScopedJavaGlobalRef(const ScopedJavaGlobalRef<T>& other) {
     this->Reset(other);
   }
 
   ScopedJavaGlobalRef(ScopedJavaGlobalRef<T>&& other) { this->swap(other); }
 
   ScopedJavaGlobalRef(JNIEnv* env, T obj) { this->Reset(env, obj); }
 
   template<typename U>
@@ skipping 55 matching lines @@
  private:
   T obj_;
 
   DISALLOW_COPY_AND_ASSIGN(JavaRefOrBare);
 };
 
 }  // namespace android
 }  // namespace base
 
 #endif  // BASE_ANDROID_SCOPED_JAVA_REF_H_