android: Fix java launcher thread

content/browser/android/launcher_thread.cc

 // Copyright 2017 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.
 
 #include "content/browser/android/launcher_thread.h"
 
 #include "jni/LauncherThread_jni.h"
 
 namespace content {
 namespace android {
 
 namespace {
 base::LazyInstance<LauncherThread>::Leaky g_launcher_thread;
 }
 
 base::MessageLoop* LauncherThread::GetMessageLoop() {
   return g_launcher_thread.Get().java_handler_thread_.message_loop();
 }
 
 LauncherThread::LauncherThread()
     : java_handler_thread_(Java_LauncherThread_getHandlerThread(
-          base::android::AttachCurrentThread())) {}
+          base::android::AttachCurrentThread())) {
+  java_handler_thread_.Start();
+}
 
 LauncherThread::~LauncherThread() {}
 
 }  // namespace android
 }  // namespace content