Reland 1: "mac: Allow Chrome to hand off its active URL to other devices."

chrome/browser/ui/cocoa/handoff_active_url_observer.h

Index: chrome/browser/ui/cocoa/handoff_active_url_observer.h
diff --git a/chrome/browser/ui/cocoa/handoff_active_url_observer.h b/chrome/browser/ui/cocoa/handoff_active_url_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..a46ed98ce6c71a01f1f4ed79ae10ffa910840ece
--- /dev/null
+++ b/chrome/browser/ui/cocoa/handoff_active_url_observer.h
@@ -0,0 +1,83 @@
+// Copyright 2014 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_UI_COCOA_HANDOFF_ACTIVE_URL_OBSERVER_H_
+#define CHROME_BROWSER_UI_COCOA_HANDOFF_ACTIVE_URL_OBSERVER_H_
+
+#include "chrome/browser/ui/browser_list_observer.h"
+#include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
+#include "content/public/browser/web_contents_observer.h"
+
+namespace content {
+class WebContents;
+}
+
+class Browser;
+class HandoffActiveURLObserverDelegate;
+class TabStripModel;
+
+// This class observes changes to the "active URL". This is defined as the
+// visible URL of the WebContents of the selected tab of the most recently
+// focused browser window.
+class HandoffActiveURLObserver : public chrome::BrowserListObserver,
+                                 public TabStripModelObserver,
+                                 public content::WebContentsObserver {
+ public:
+  explicit HandoffActiveURLObserver(HandoffActiveURLObserverDelegate* delegate);
+  ~HandoffActiveURLObserver() override;
+
+ private:
+  // chrome::BrowserListObserver
+  void OnBrowserSetLastActive(Browser* browser) override;
+  void OnBrowserRemoved(Browser* browser) override;
+
+  // TabStripModelObserver
+  void ActiveTabChanged(content::WebContents* old_contents,
+                        content::WebContents* new_contents,
+                        int index,
+                        int reason) override;
+  void TabStripModelDeleted() override;
+
+  // content::WebContentsObserver
+  void DidNavigateMainFrame(
+      const content::LoadCommittedDetails& details,
+      const content::FrameNavigateParams& params) override;
+  void WebContentsDestroyed() override;
+
+  // This method ensures that the instance is registered as an observer of the
+  // correct TabStripModel and WebContents for |active_browser_|.
+  void UpdateObservations();
+
+  // Makes this object start observing the TabStripModel, if it is not already
+  // doing so. This method is idempotent.
+  void StartObservingTabStripModel(TabStripModel* tab_strip_model);
+
+  // Makes this object stop observing the TabStripModel.
+  void StopObservingTabStripModel();
+
+  // Makes this object start observing the WebContents, if it is not already
+  // doing so. This method is idempotent.
+  void StartObservingWebContents(content::WebContents* web_contents);
+
+  // Makes this object stop observing the WebContents.
+  void StopObservingWebContents();
+
+  // Returns the active WebContents. May return nullptr.
+  content::WebContents* GetActiveWebContents();
+
+  // Instances of this class should be owned by their |delegate_|.
+  HandoffActiveURLObserverDelegate* delegate_;
+
+  // When this pointer is not nullptr, this object is registered as an observer
+  // of the TabStripModel.
+  TabStripModel* active_tab_strip_model_;
+
+  // This pointer is always up to date, and points to the most recently
+  // activated browser, or nullptr if no browsers exist.
+  Browser* active_browser_;
+
+  DISALLOW_COPY_AND_ASSIGN(HandoffActiveURLObserver);
+};
+
+#endif  // CHROME_BROWSER_UI_COCOA_HANDOFF_ACTIVE_URL_OBSERVER_H_