cros: Enable WebUILoginView reuse.

chrome/browser/chromeos/login/ui/shared_web_view_factory.cc

+// Copyright 2016 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/chromeos/login/ui/shared_web_view_factory.h"
+
+#include "chrome/browser/chromeos/login/ui/shared_web_view.h"
+#include "chrome/browser/profiles/incognito_helpers.h"
+#include "chrome/browser/profiles/profile.h"
+#include "components/keyed_service/content/browser_context_dependency_manager.h"
+
+namespace chromeos {
+
+// static
+SharedWebView* SharedWebViewFactory::GetForProfile(Profile* profile) {
+  auto result = static_cast<SharedWebView*>(
+      GetInstance()->GetServiceForBrowserContext(profile, true));
+  return result;
+}
+
+// static
+SharedWebViewFactory* SharedWebViewFactory::GetInstance() {
+  return base::Singleton<SharedWebViewFactory>::get();
+}
+
+SharedWebViewFactory::SharedWebViewFactory()
+    : BrowserContextKeyedServiceFactory(
+          "SharedWebViewFactory",
+          BrowserContextDependencyManager::GetInstance()) {}
+
+SharedWebViewFactory::~SharedWebViewFactory() {}
+
+content::BrowserContext* SharedWebViewFactory::GetBrowserContextToUse(
+    content::BrowserContext* context) const {
+  // This matches the logic in ExtensionSyncServiceFactory, which uses the
+  // orginal browser context.
+  return chrome::GetBrowserContextRedirectedInIncognito(context);

[xiyuan, 2016/12/09 22:37:30]

|context| should be the incognito sign-in profile and we should use that as-is.
Otherwise, we would create a WebView use the original profile which is backed by
disk and we don't have to leave traces for login.

And we might consider check |context| is a sign-in profile and only use that.

i.e.

  // No SharedWebView if |context| is not sign-in profile.
  if (Profile::FromBrowserContext(context) != ProfileHelper::GetSigninProfile())
    return nullptr;

  return context;

[jdufault, 2016/12/12 18:23:09]

Done.

+}
+
+KeyedService* SharedWebViewFactory::BuildServiceInstanceFor(
+    content::BrowserContext* context) const {
+  // By default, no service instances are built for the signin profile since it
+  // is considered incognito.

[xiyuan, 2016/12/09 22:37:30]

After we override GetBrowserContextToUse above, this should be called for
incognito profile. So the comment is not exactly correct. Update or remove.

[jdufault, 2016/12/12 18:23:09]

Done.

+  return new SharedWebView(Profile::FromBrowserContext(context));
+}
+
+}  // namespace chromeos