Use JavaObjectWeakGlobalRef in ContentViewCore.

base/android/jni_helper.cc

 // 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.
 
 #include "base/android/jni_helper.h"
 
 #include "base/android/jni_android.h"
 #include "base/logging.h"
 
 using base::android::AttachCurrentThread;
 
 JavaObjectWeakGlobalRef::JavaObjectWeakGlobalRef(JNIEnv* env, jobject obj)
     : obj_(env->NewWeakGlobalRef(obj)) {
   DCHECK(obj_);
 }
 
 JavaObjectWeakGlobalRef::~JavaObjectWeakGlobalRef() {
-  DCHECK(obj_);
-  AttachCurrentThread()->DeleteWeakGlobalRef(obj_);
+  reset();
+}
+
+void JavaObjectWeakGlobalRef::reset() {
+  if (obj_) {
+    AttachCurrentThread()->DeleteWeakGlobalRef(obj_);
+    obj_ = NULL;
+  }
 }
 
 base::android::ScopedJavaLocalRef<jobject>
     JavaObjectWeakGlobalRef::get(JNIEnv* env) const {
   return GetRealObject(env, obj_);
 }
 
 base::android::ScopedJavaLocalRef<jobject> GetRealObject(
-    JNIEnv* env, jobject obj) {
-  jobject real = env->NewLocalRef(obj);
-  if (!real)
-    DLOG(ERROR) << "The real object has been deleted!";
+    JNIEnv* env, jweak obj) {
+  jobject real = NULL;
+  if (obj) {
+    real = env->NewLocalRef(obj);
+    if (!real)
+      DLOG(ERROR) << "The real object has been deleted!";
+  }
   return base::android::ScopedJavaLocalRef<jobject>(env, real);
 }