Remove redundant field initialization in Java code.

content/public/android/java/src/org/chromium/content/browser/MemoryMonitorAndroid.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.content.browser;
 
 import android.app.ActivityManager;
 import android.content.ComponentCallbacks2;
 import android.content.Context;
 import android.content.res.Configuration;
 
 import org.chromium.base.Log;
 import org.chromium.base.annotations.CalledByNative;
 import org.chromium.base.annotations.JNINamespace;
 
 /**
  * Android implementation of MemoryMonitor.
  */
 @JNINamespace("content")
 class MemoryMonitorAndroid {
     private static final String TAG = "MemoryMonitorAndroid";
     private static final ActivityManager.MemoryInfo sMemoryInfo =
             new ActivityManager.MemoryInfo();
-    private static ComponentCallbacks2 sCallbacks = null;
+    private static ComponentCallbacks2 sCallbacks;
 
     private MemoryMonitorAndroid() {
     }
 
     /**
      * Get the current MemoryInfo from ActivityManager and invoke the native
      * callback to populate the MemoryInfo.
      *
      * @param context The context of the application.
      * @param outPtr A native output pointer to populate MemoryInfo. This is
@@ skipping 45 matching lines @@
             };
         context.registerComponentCallbacks(sCallbacks);
     }
 
     private static native void nativeGetMemoryInfoCallback(
             long availMem, boolean lowMemory,
             long threshold, long totalMem, long outPtr);
 
     private static native void nativeOnTrimMemory(int level);
 }