[fsp] Simplify browser tests by extracting the common code.

chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_apitest.cc

 // Copyright 2013 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 "chrome/browser/extensions/extension_apitest.h"
 
 namespace extensions {
 
 class FileSystemProviderApiTest : public ExtensionApiTest {
  public:
   FileSystemProviderApiTest()
       // Set the channel to "trunk" since this API is restricted to trunk.
       : current_channel_(chrome::VersionInfo::CHANNEL_UNKNOWN) {
   }
 
+  // Loads a helper testing extension.
+  virtual void SetUpOnMainThread() OVERRIDE {
+    ExtensionApiTest::SetUpOnMainThread();
+    const extensions::Extension* extension = LoadExtensionWithFlags(
+        test_data_dir_.AppendASCII("file_system_provider/test_util"),
+        kFlagEnableIncognito);
+    ASSERT_TRUE(extension);
+  }
+
  private:
   extensions::ScopedCurrentChannel current_channel_;
 };
 
 IN_PROC_BROWSER_TEST_F(FileSystemProviderApiTest, Mount) {
   ASSERT_TRUE(RunPlatformAppTestWithFlags("file_system_provider/mount",
                                           kFlagLoadAsComponent))
       << message_;
 }
 
@@ skipping 33 matching lines @@
       << message_;
 }
 
 IN_PROC_BROWSER_TEST_F(FileSystemProviderApiTest, MimeType) {
   ASSERT_TRUE(RunPlatformAppTestWithFlags("file_system_provider/mime_type",
                                           kFlagLoadAsComponent))
       << message_;
 }
 
 }  // namespace extensions