Ensure ShellExtensionSystem::Init() is called in all extensions_browsertests.

extensions/shell/test/shell_test.cc

 // 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.
 
 #include "extensions/shell/test/shell_test.h"
 
 #include "base/base_paths.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
@@ skipping 38 matching lines @@
   command_line->AppendSwitchASCII(switches::kTestType, "appshell");
   SetUpCommandLine(command_line);
   content::BrowserTestBase::SetUp();
 }
 
 void AppShellTest::SetUpOnMainThread() {
   browser_context_ = ShellContentBrowserClient::Get()->GetBrowserContext();
 
   extension_system_ = static_cast<ShellExtensionSystem*>(
       ExtensionSystem::Get(browser_context_));
+  extension_system_->Init();
 }
 
 void AppShellTest::RunTestOnMainThreadLoop() {
   DCHECK(base::MessageLoopForUI::IsCurrent());
   base::RunLoop().RunUntilIdle();
 
   SetUpOnMainThread();
 
   RunTestOnMainThread();
 
   TearDownOnMainThread();
 
   // Clean up the app window.
   DesktopController::instance()->CloseAppWindows();
 }
 
 }  // namespace extensions