Remove redundant field initialization in Java code.

components/gcm_driver/instance_id/android/java/src/org/chromium/components/gcm_driver/instance_id/InstanceIDWithSubtype.java

 // Copyright 2016 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.instance_id;
 
 import android.content.Context;
 import android.text.TextUtils;
 
 import com.google.android.gms.iid.InstanceID;
@@ skipping 13 matching lines @@
     private final String mSubtype;
 
     /** Cached instances. May be accessed from multiple threads; synchronize on InstanceID.class. */
     @VisibleForTesting
     @SuppressFBWarnings("MS_MUTABLE_COLLECTION_PKGPROTECT")
     public static final Map<String, InstanceIDWithSubtype> sSubtypeInstances = new HashMap<>();
 
     /** Fake subclasses can set this so getInstance creates instances of them. */
     @VisibleForTesting
     @SuppressFBWarnings("MS_SHOULD_BE_FINAL")
-    protected static FakeFactory sFakeFactoryForTesting = null;
+    protected static FakeFactory sFakeFactoryForTesting;
 
     protected InstanceIDWithSubtype(Context context, String subtype) {
         super(context, subtype, null /* options */);
         mSubtype = subtype;
     }
 
     /**
      * Returns an instance of this class. Unlike {@link InstanceID#getInstance(Context)}, it is not
      * a singleton, but instead a different instance will be returned for each {@code subtype}.
      */
@@ skipping 38 matching lines @@
     public String getSubtype() {
         return mSubtype;
     }
 
     /** Fake subclasses can set {@link #sFakeFactoryForTesting} to an implementation of this. */
     @VisibleForTesting
     public interface FakeFactory {
         public InstanceIDWithSubtype create(Context context, String subtype);
     }
 }