[Android] Add gn support for multidex.

base/android/java/templates/ChromiumMultiDex.template

 // Copyright 2015 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.multidex;
 
 import android.content.Context;
 import android.os.Build;
 import android.os.Process;
 import android.support.multidex.MultiDex;
 
 import org.chromium.base.Log;
 import org.chromium.base.VisibleForTesting;
 
 import java.lang.reflect.InvocationTargetException;
 
 /**
  *  Performs multidex installation for non-isolated processes.
  */
 public class ChromiumMultiDex {
 
     private static final String TAG = "base_multidex";
 
     /**
-     *  Installs secondary dexes if possible.
+     *  Installs secondary dexes if possible/necessary.
      *
      *  Isolated processes (e.g. renderer processes) can't load secondary dex files on
      *  K and below, so we don't even try in that case.
      *
+     *  In release builds, this is a no-op because:
+     *    - multidex isn't necessary in release builds because we run proguard there and
+     *      thus aren't threatening to hit the dex limit; and
+     *    - calling MultiDex.install, even in the absence of secondary dexes, causes a
+     *      significant regression in start-up time (crbug.com/525695).
+     *
      *  @param context The application context.
      */
     @VisibleForTesting
-#if defined(CONFIGURATION_NAME_Debug)
+#if defined(MULTIDEX_CONFIGURATION_Debug)
     public static void install(Context context) {
         try {
             // TODO(jbudorick): Back out this version check once support for K & below works.
             // http://crbug.com/512357
             if (Build.VERSION.SDK_INT < Build.VERSION_CODES.LOLLIPOP && processIsIsolated()) {
                 Log.i(TAG, "Skipping multidex installation: inside isolated process.");
             } else {
                 MultiDex.install(context);
                 Log.i(TAG, "Completed multidex installation.");
             }
@@ skipping 10 matching lines @@
     private static boolean processIsIsolated()
             throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
         return (boolean) Process.class.getMethod("isIsolated").invoke(null);
     }
 #else
     public static void install(Context context) {
     }
 #endif
 
 }