[Chromecast] Add CastWebView::Observer

Adds an observer interface for CastWebView. This allows multiple
components to track the CastWebView lifecycle (similar to
WebContentsObserver APIs).

Bug: None
Test: cast_shell
Change-Id: I37f45b896c1696c9fe91d9706cbddf0b2e46d2cc
Reviewed-on: https://chromium-review.googlesource.com/961588Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Sean Topping <seantopping@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543179}

chromecast/browser/BUILD.gn

@@ -46,6 +46,7 @@ cast_source_set("browser") {
     "cast_resource_dispatcher_host_delegate.h",
     "cast_web_contents_manager.cc",
     "cast_web_contents_manager.h",
+    "cast_web_view.cc",
     "cast_web_view.h",
     "cast_web_view_default.cc",
     "cast_web_view_default.h",

chromecast/browser/cast_web_view.cc

+// Copyright 2018 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 "chromecast/browser/cast_web_view.h"
+
+namespace chromecast {
+
+CastWebView::CastWebView() {}
+
+CastWebView::~CastWebView() {
+  for (Observer& observer : observer_list_) {
+    observer.OnPageDestroyed(this);
+  }
+}
+
+void CastWebView::AddObserver(CastWebView::Observer* observer) {
+  observer_list_.AddObserver(observer);
+}
+
+void CastWebView::RemoveObserver(CastWebView::Observer* observer) {
+  observer_list_.RemoveObserver(observer);
+}
+
+}  // namespace chromecast

chromecast/browser/cast_web_view.h

@@ -8,6 +8,8 @@
 #include <cstdint>
 #include <string>
 
+#include "base/macros.h"
+#include "base/observer_list.h"
 #include "base/strings/string16.h"
 #include "base/time/time.h"
 #include "chromecast/browser/cast_content_window.h"
@@ -42,6 +44,17 @@ class CastWebView {
         const base::string16& source_id) = 0;
   };
 
+  // Observer interface for tracking CastWebView lifetime.
+  class Observer {
+   public:
+    // Notifies that |web_view| is being destroyed. |web_view| should be assumed
+    // invalid after this method returns.
+    virtual void OnPageDestroyed(CastWebView* web_view) {}
+
+   protected:
+    virtual ~Observer() {}
+  };
+
   // The parameters used to create a CastWebView instance. Passed to
   // CastWebContentsManager::CreateWebView().
   struct CreateParams {
@@ -69,7 +82,8 @@ class CastWebView {
     bool enabled_for_dev = false;
   };
 
-  virtual ~CastWebView() {}
+  CastWebView();
+  virtual ~CastWebView();
 
   virtual shell::CastContentWindow* window() const = 0;
 
@@ -89,6 +103,15 @@ class CastWebView {
   // |is_visible| is true.
   virtual void CreateWindow(CastWindowManager* window_manager,
                             bool is_visible) = 0;
+
+  // Observer interface:
+  void AddObserver(Observer* observer);
+  void RemoveObserver(Observer* observer);
+
+ private:
+  base::ObserverList<Observer> observer_list_;
+
+  DISALLOW_COPY_AND_ASSIGN(CastWebView);
 };
 
 }  // namespace chromecast