Add @MainDex annotation to classes used in child processes.

base/android/java/src/org/chromium/base/TimeUtils.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.base;
 
 import org.chromium.base.annotations.JNINamespace;
+import org.chromium.base.annotations.MainDex;
 
 /** Time-related utilities. */
 @JNINamespace("base::android")
+@MainDex
 public class TimeUtils {
     private TimeUtils() {}
 
     /** Returns TimeTicks::Now() in microseconds. */
     public static native long nativeGetTimeTicksNowUs();
 }