Allow posting the CronetEngine UI Thread initialization on a custom Ui executor instead of the defa…

components/cronet/android/java/src/org/chromium/net/impl/CronetUrlRequestContext.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.impl;
 
 import android.os.ConditionVariable;
 import android.os.Handler;
 import android.os.Looper;
 import android.os.Process;
@@ skipping 160 matching lines @@
                     // initialization on main and network threads completes and
                     // initNetworkThread is called back on network thread.
                     nativeInitRequestContextOnMainThread(mUrlRequestContextAdapter);
                 }
             }
         };
         // Run task immediately or post it to the UI thread.
         if (Looper.getMainLooper() == Looper.myLooper()) {
             task.run();
         } else {
-            new Handler(Looper.getMainLooper()).post(task);
+            if (builder.uiExecutor() != null) {
+                builder.uiExecutor().execute(task);
+            } else {
+                new Handler(Looper.getMainLooper()).post(task);
+            }
         }
     }
 
     @VisibleForTesting
     public static long createNativeUrlRequestContextConfig(CronetEngineBuilderImpl builder) {
         final long urlRequestContextConfig = nativeCreateRequestContextConfig(
                 builder.getUserAgent(), builder.storagePath(), builder.quicEnabled(),
                 builder.getDefaultQuicUserAgentId(), builder.http2Enabled(), builder.sdchEnabled(),
                 builder.dataReductionProxyKey(), builder.dataReductionProxyPrimaryProxy(),
                 builder.dataReductionProxyFallbackProxy(),
@@ skipping 533 matching lines @@
     @NativeClassQualifiedName("CronetURLRequestContextAdapter")
     private native void nativeProvideRTTObservations(long nativePtr, boolean should);
 
     @NativeClassQualifiedName("CronetURLRequestContextAdapter")
     private native void nativeProvideThroughputObservations(long nativePtr, boolean should);
 
     public boolean isNetworkThread(Thread thread) {
         return thread == mNetworkThread;
     }
 }