[Cronet] Remove JSON serialization of CronetEngine.Builder

components/cronet/android/api/src/org/chromium/net/HttpUrlConnectionUrlRequestFactory.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.net;
 
 import android.content.Context;
+import android.text.TextUtils;
 
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.nio.channels.WritableByteChannel;
 import java.util.Map;
 
 /**
  * Network request using {@link java.net.HttpURLConnection}.
  * @deprecated Use {@link CronetEngine} instead.
  */
 @Deprecated
 class HttpUrlConnectionUrlRequestFactory extends HttpUrlRequestFactory {
 
     private final Context mContext;
     private final String mDefaultUserAgent;
 
     public HttpUrlConnectionUrlRequestFactory(Context context, CronetEngine.Builder config) {
         mContext = context;
         String userAgent = config.getUserAgent();
-        if (userAgent.isEmpty()) {
+        if (TextUtils.isEmpty(userAgent)) {
             // Cannot use config.getDefaultUserAgent() as config.mContext may be null.
             userAgent = new CronetEngine.Builder(mContext).getDefaultUserAgent();
         }
         mDefaultUserAgent = userAgent;
     }
 
     @Override
     public boolean isEnabled() {
         return true;
     }
@@ skipping 26 matching lines @@
             out.close();
         } catch (IOException e) {
             // Ignore any exceptions.
         }
     }
 
     @Override
     public void stopNetLog() {
     }
 }