Always load signin profile on Chrome OS startup.

chrome/browser/chromeos/file_manager/external_filesystem_apitest.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/bind.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/path_service.h"
 #include "chrome/browser/browser_process.h"
@@ skipping 511 matching lines @@
   // FileSystemExtensionApiTestBase override.
   void TearDown() override {
     FileSystemExtensionApiTestBase::TearDown();
     ui::SelectFileDialog::SetFactory(NULL);
   }
 
  protected:
   // DriveIntegrationService factory function for this test.
   drive::DriveIntegrationService* CreateDriveIntegrationService(
       Profile* profile) {
+    // Ignore signin profile.
+    if (profile->GetPath() == chromeos::ProfileHelper::GetSigninProfileDir())
+      return NULL;
+
+    // DriveFileSystemExtensionApiTest doesn't expect that several user profiles
+    // could exist simultaneously.
+    CHECK(fake_drive_service_ == NULL);
     fake_drive_service_ = new drive::FakeDriveService;
     fake_drive_service_->LoadAppListForDriveApi("drive/applist.json");
 
     std::map<std::string, std::string> resource_ids;
     EXPECT_TRUE(InitializeDriveService(fake_drive_service_, &resource_ids));
 
     return new drive::DriveIntegrationService(
         profile, NULL, fake_drive_service_, "", test_cache_root_.path(), NULL);
   }
 
@@ skipping 301 matching lines @@
                        AppFileHandlerMulti) {
   EXPECT_TRUE(
       RunFileSystemExtensionApiTest("file_browser/app_file_handler_multi",
                                     FILE_PATH_LITERAL("manifest.json"),
                                     "",
                                     FLAGS_NONE))
       << message_;
 }
 }  // namespace
 }  // namespace file_manager