Create a ChromeBrowserHostImpl for every Chrome tab (see issue #2969)

The Browser object represents the top-level Chrome browser window. One or more
tabs (WebContents) are then owned by the Browser object via TabStripModel. A
new Browser object can be created programmatically using "new Browser" or
Browser::Create, or as a result of user action such as dragging a tab out of an
existing window. New or existing tabs can also be added to an already existing
Browser object.

The Browser object acts as the WebContentsDelegate for all attached tabs. CEF
integration requires WebContentsDelegate callbacks and notification of tab
attach/detach. To support this integration we add a cef::BrowserDelegate
(ChromeBrowserDelegate) member that is created in the Browser constructor and
receives delegation for the Browser callbacks. ChromeBrowserDelegate creates a
new ChromeBrowserHostImpl when a tab is added to a Browser for the first time,
and that ChromeBrowserHostImpl continues to exist until the tab's WebContents
is destroyed. The associated WebContents object does not change, but the
Browser object will change when the tab is dragged between windows.

CEF callback logic is shared between the chrome and alloy runtimes where
possible. This shared logic has been extracted from CefBrowserHostImpl to
create new CefBrowserHostBase and CefBrowserContentsDelegate classes. The
CefBrowserHostImpl class is now only used with the alloy runtime and will be
renamed to AlloyBrowserHostImpl in a future commit.

libcef/browser/chrome/chrome_browser_delegate.h

@@ -0,0 +1,80 @@
+// Copyright 2020 The Chromium Embedded Framework 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 CEF_LIBCEF_BROWSER_CHROME_CHROME_BROWSER_DELEGATE_H_
+#define CEF_LIBCEF_BROWSER_CHROME_CHROME_BROWSER_DELEGATE_H_
+#pragma once
+
+#include <memory>
+
+#include "libcef/browser/browser_host_base.h"
+#include "libcef/browser/browser_info.h"
+#include "libcef/browser/chrome/browser_delegate.h"
+
+#include "base/optional.h"
+
+class CefBrowserContentsDelegate;
+class CefRequestContextImpl;
+class ChromeBrowserHostImpl;
+
+// Implementation of the cef::BrowserDelegate interface. Lifespan is controlled
+// by the Browser object. Only accessed on the UI thread.
+//
+// The Browser object represents the top-level Chrome browser window. One or
+// more tabs (WebContents) are then owned by the Browser object via
+// TabStripModel. A new Browser object can be created programmatically using
+// "new Browser" or Browser::Create, or as a result of user action such as
+// dragging a tab out of an existing window. New or existing tabs can also be
+// added to an already existing Browser object.
+//
+// The Browser object acts as the WebContentsDelegate for all attached tabs. CEF
+// integration requires WebContentsDelegate callbacks and notification of tab
+// attach/detach. To support this integration a cef::BrowserDelegate
+// (ChromeBrowserDelegate) member is created in the Browser constructor and
+// receives delegation for the Browser callbacks. ChromeBrowserDelegate creates
+// a new ChromeBrowserHostImpl when a tab is added to a Browser for the first
+// time, and that ChromeBrowserHostImpl continues to exist until the tab's
+// WebContents is destroyed. The associated WebContents object does not change,
+// but the Browser object will change when the tab is dragged between windows.
+class ChromeBrowserDelegate : public cef::BrowserDelegate {
+ public:
+  ChromeBrowserDelegate(Browser* browser,
+                        const CefBrowserHostBase::CreateParams& create_params);
+  ~ChromeBrowserDelegate() override;
+
+  // cef::BrowserDelegate methods:
+  void SetAsDelegate(content::WebContents* web_contents,
+                     bool set_delegate) override;
+
+  // WebContentsDelegate methods:
+  void LoadingStateChanged(content::WebContents* source,
+                           bool to_different_document) override;
+  void UpdateTargetURL(content::WebContents* source, const GURL& url) override;
+  bool DidAddMessageToConsole(content::WebContents* source,
+                              blink::mojom::ConsoleMessageLevel log_level,
+                              const base::string16& message,
+                              int32_t line_no,
+                              const base::string16& source_id) override;
+  void DidNavigateMainFramePostCommit(
+      content::WebContents* web_contents) override;
+  void EnterFullscreenModeForTab(
+      content::RenderFrameHost* requesting_frame,
+      const blink::mojom::FullscreenOptions& options) override;
+  void ExitFullscreenModeForTab(content::WebContents* web_contents) override;
+
+  Browser* browser() const { return browser_; }
+
+ private:
+  CefBrowserContentsDelegate* GetDelegateForWebContents(
+      content::WebContents* web_contents);
+
+  Browser* const browser_;
+
+  // Used when creating a new browser host.
+  const CefBrowserHostBase::CreateParams create_params_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChromeBrowserDelegate);
+};
+
+#endif  // CEF_LIBCEF_BROWSER_CHROME_CHROME_BROWSER_DELEGATE_H_