Small improvements to JNI references.

base/android/jni_weak_ref.h

 // Copyright 2014 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_JNI_WEAK_REF_H_
 #define BASE_ANDROID_JNI_WEAK_REF_H_
 
 #include <jni.h>
 
 #include "base/android/scoped_java_ref.h"
 #include "base/base_export.h"
 
 // Manages WeakGlobalRef lifecycle.
 // This class is not thread-safe w.r.t. get() and reset(). Multiple threads may
 // safely use get() concurrently, but if the user calls reset() (or of course,
 // calls the destructor) they'll need to provide their own synchronization.
 class BASE_EXPORT JavaObjectWeakGlobalRef {
  public:
   JavaObjectWeakGlobalRef();
   JavaObjectWeakGlobalRef(const JavaObjectWeakGlobalRef& orig);
+  JavaObjectWeakGlobalRef(JavaObjectWeakGlobalRef&& orig);
   JavaObjectWeakGlobalRef(JNIEnv* env, jobject obj);
+  JavaObjectWeakGlobalRef(JNIEnv* env,
+                          const base::android::JavaRef<jobject>& obj);
   virtual ~JavaObjectWeakGlobalRef();
 
   void operator=(const JavaObjectWeakGlobalRef& rhs);
+  void operator=(JavaObjectWeakGlobalRef&& rhs);
 
   base::android::ScopedJavaLocalRef<jobject> get(JNIEnv* env) const;
 
-  bool is_empty() const { return obj_ == NULL; }
+  bool is_empty() const { return obj_ == nullptr; }
 
   void reset();
 
  private:
   void Assign(const JavaObjectWeakGlobalRef& rhs);
 
   jweak obj_;
 };
 
 // Get the real object stored in the weak reference returned as a
 // ScopedJavaLocalRef.
 BASE_EXPORT base::android::ScopedJavaLocalRef<jobject> GetRealObject(
     JNIEnv* env, jweak obj);
 
 #endif  // BASE_ANDROID_JNI_WEAK_REF_H_