Remove redundant field initialization in Java code.

components/gcm_driver/android/java/src/org/chromium/components/gcm_driver/GCMDriver.java

 // 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.
 
 package org.chromium.components.gcm_driver;
 
 import android.content.Context;
 import android.os.AsyncTask;
 import android.os.Bundle;
 
@@ skipping 12 matching lines @@
  * It uses Android's Java GCM APIs to implement GCM registration etc, and
  * sends back GCM messages over JNI.
  *
  * Threading model: all calls to/from C++ happen on the UI thread.
  */
 @JNINamespace("gcm")
 public class GCMDriver {
     private static final String TAG = "GCMDriver";
 
     // The instance of GCMDriver currently owned by a C++ GCMDriverAndroid, if any.
-    private static GCMDriver sInstance = null;
+    private static GCMDriver sInstance;
 
     private long mNativeGCMDriverAndroid;
     private final Context mContext;
     private GoogleCloudMessagingSubscriber mSubscriber;
 
     private GCMDriver(long nativeGCMDriverAndroid, Context context) {
         mNativeGCMDriverAndroid = nativeGCMDriverAndroid;
         mContext = context;
         mSubscriber = new GoogleCloudMessagingV2(context);
     }
@@ skipping 115 matching lines @@
         sInstance.mSubscriber = subscriber;
     }
 
     private native void nativeOnRegisterFinished(long nativeGCMDriverAndroid, String appId,
             String registrationId, boolean success);
     private native void nativeOnUnregisterFinished(long nativeGCMDriverAndroid, String appId,
             boolean success);
     private native void nativeOnMessageReceived(long nativeGCMDriverAndroid, String appId,
             String senderId, String collapseKey, byte[] rawData, String[] dataKeysAndValues);
 }