cros: Enable WebUILoginView reuse.

chrome/browser/chromeos/login/ui/shared_web_view.h

+// 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.
+
+#ifndef CHROME_BROWSER_CHROMEOS_LOGIN_UI_SHARED_WEB_VIEW_H_
+#define CHROME_BROWSER_CHROMEOS_LOGIN_UI_SHARED_WEB_VIEW_H_
+
+#include <memory>
+
+#include "base/macros.h"
+#include "base/memory/memory_pressure_listener.h"
+#include "base/memory/ref_counted.h"
+#include "components/keyed_service/core/keyed_service.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
+#include "url/gurl.h"
+
+class Profile;
+
+namespace chromeos {
+
+class WebViewHandle;
+
+// Stores and fetches a views::WebView instance owned by the current user's
+// profile. This allows for a WebView to be reused over time or preloaded. Use

[xiyuan, 2016/12/12 18:51:11]

"the current user's profile" -> the sign-in profile since SharedWebView is used
to share the webview for login/lock screen.

[jdufault, 2016/12/12 19:50:27]

Done.

+// SharedWebViewFactory to get an instance of this class per profile.
+class SharedWebView : public KeyedService,
+                      public content::NotificationObserver {
+ public:
+  explicit SharedWebView(Profile* profile);
+  ~SharedWebView() override;
+  void Shutdown() override;
+
+  // Stores a webview instance inside of |out_handle|. |url| is the initial
+  // URL that the webview stores (note: this function does not perform the
+  // navigation). This returns true if the webview was reused, false if it
+  // was freshly created.
+  bool Get(const GURL& url, scoped_refptr<WebViewHandle>* out_handle);
+
+ private:
+  // content::NotificationObserver:
+  void Observe(int type,
+               const content::NotificationSource& source,
+               const content::NotificationDetails& details) override;
+
+  // Called when there is a memory pressure event.
+  void OnMemoryPressure(
+      base::MemoryPressureListener::MemoryPressureLevel level);
+
+  content::NotificationRegistrar registrar_;
+
+  // Profile used for creating the views::WebView instance.
+  Profile* const profile_;
+
+  // Cached URL that the |web_view_| instance should point to used for
+  // validation.
+  GURL web_view_url_;
+
+  // Shared web-view instance. Callers may take a reference on the handle so it
+  // could outlive this class.
+  scoped_refptr<WebViewHandle> web_view_handle_;
+
+  std::unique_ptr<base::MemoryPressureListener> memory_pressure_listener_;
+
+  DISALLOW_COPY_AND_ASSIGN(SharedWebView);
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_LOGIN_UI_SHARED_WEB_VIEW_H_