If Chrome Binaries version > App Host version, then update App Host.

chrome/browser/extensions/app_host/app_host_main.cc

 // Copyright (c) 2012 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 "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/file_path.h"
 #include "base/logging.h"
 #include "base/process_util.h"
 #include "chrome/browser/extensions/app_host/binaries_installer.h"
+#include "chrome/browser/extensions/app_host/update.h"
 #include "chrome/installer/launcher_support/chrome_launcher_support.h"
 
 int main(int /* argc */, char* /* argv[] */) {
   base::AtExitManager exit_manager;
 
   // Initialize the commandline singleton from the environment.
   CommandLine::Init(0, NULL);
 
   FilePath chrome_exe(chrome_launcher_support::GetAnyChromePath());
-
   if (chrome_exe.empty()) {
     LOG(INFO) << "No Chrome executable could be found. Let's install it.";
     HRESULT hr = app_host::InstallBinaries();
     if (FAILED(hr)) {
       LOG(ERROR) << "Failed to install the Chrome Binaries. Error: " << hr;
       return 1;
     } else {
       chrome_exe = chrome_launcher_support::GetAnyChromePath();
       if (chrome_exe.empty()) {
         LOG(ERROR) << "Failed to find the Chrome Binaries despite a "
                    << "'successful' installation.";
         return 1;
       }
     }
   }
 
   CommandLine chrome_exe_command_line(chrome_exe);
   chrome_exe_command_line.AppendArguments(
       *CommandLine::ForCurrentProcess(), false);
+  // Launch Chrome before checking for update, for faster user experience.
+  bool launch_result = base::LaunchProcess(chrome_exe_command_line,
+                                           base::LaunchOptions(),
+                                           NULL);
+  if (launch_result)
+    LOG(INFO) << "Delegated to Chrome executable at " << chrome_exe.value();
+  else
+    LOG(INFO) << "Failed to launch Chrome executable at " << chrome_exe.value();
 
-  if (base::LaunchProcess(chrome_exe_command_line,
-                          base::LaunchOptions(),
-                          NULL)) {
-    LOG(INFO) << "Delegated to Chrome executable at " << chrome_exe.value();
-    return 0;
-  } else {
-    LOG(INFO) << "Failed to launch Chrome executable at " << chrome_exe.value();
-    return 1;
-  }
+  app_host::EnsureAppHostUpToDate();
+
+  return !launch_result;
 }