Browser Plugin: Implement CanGoBack/CanGoForward

content/renderer/browser_plugin/browser_plugin.h

 // Copyright (c) 2012 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  CONTENT_RENDERER_BROWSER_PLUGIN_BROWSER_PLUGIN_H_
 #define  CONTENT_RENDERER_BROWSER_PLUGIN_BROWSER_PLUGIN_H_
 
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebPlugin.h"
 
 #include "base/memory/scoped_ptr.h"
@@ skipping 22 matching lines @@
   // Get the src attribute value of the BrowserPlugin instance if the guest
   // has not crashed.
   std::string GetSrcAttribute() const;
   // Set the src attribute value of the BrowserPlugin instance and reset
   // the guest_crashed_ flag.
   void SetSrcAttribute(const std::string& src);
   // Returns Chrome's process ID for the current guest.
   int process_id() const { return process_id_; }
   // The partition identifier string is stored as UTF-8.
   std::string GetPartitionAttribute() const;
+  // Query whether the guest can navigate back to the previous entry.
+  bool CanGoBack() const;
+  // Query whether the guest can navigation forward to the next entry.
+  bool CanGoForward() const;
   // This method can be successfully called only before the first navigation for
   // this instance of BrowserPlugin. If an error occurs, the |error_message| is
   // set appropriately to indicate the failure reason.
   bool SetPartitionAttribute(const std::string& partition_id,
                              std::string& error_message);
 
   // Inform the BrowserPlugin to update its backing store with the pixels in
   // its damage buffer.
   void UpdateRect(int message_id,
                   const BrowserPluginMsg_UpdateRect_Params& params);
   // Inform the BrowserPlugin that its guest has crashed.
   void GuestCrashed();
   // Informs the BrowserPlugin that the guest has navigated to a new URL.
   void DidNavigate(const GURL& url, int process_id);
+  // Informs the BrowserPlugin that the guest's navigation state has changed.
+  void NavigationStateUpdate(int current_entry_index, int entry_count);

[Charlie Reis, 2012/10/10 06:06:53]

Seems like this can just be merged into DidNavigate.

[Fady Samuel, 2012/10/10 17:36:44]

Done.

   // Inform the BrowserPlugin that the guest has started loading a new page.
   void LoadStart(const GURL& url, bool is_top_level);
   // Inform the BrowserPlugin that the guest has aborted loading a new page.
   void LoadAbort(const GURL& url, bool is_top_level, const std::string& type);
   // Inform the BrowserPlugin that the guest has redirected a navigation.
   void LoadRedirect(const GURL& old_url,
                     const GURL& new_url,
                     bool is_top_level);
   // Tells the BrowserPlugin to advance the focus to the next (or previous)
   // element.
@@ skipping 126 matching lines @@
   bool persist_storage_;
   // Tracks the visibility of the browser plugin regardless of the whole
   // embedder RenderView's visibility.
   bool visible_;
   typedef std::vector<v8::Persistent<v8::Function> > EventListeners;
   typedef std::map<std::string, EventListeners> EventListenerMap;
   EventListenerMap event_listener_map_;
 #if defined(OS_WIN)
   base::SharedMemory shared_memory_;
 #endif
+  int current_nav_entry_index_;
+  int nav_entry_count_;

[Charlie Reis, 2012/10/10 06:06:53]

I get really scared by keeping this state here, but I don't see another way to
implement it without having an asynchronous reply.  We need to avoid having this
grow into more history state that could lead to broken navigation in apps,
though.  Maybe it's overkill, but I suggest the following warning comment above
these two fields:

Important: Do not add more history state here.
We strongly discourage storing additional history state (such as page IDs) in
the embedder process, at the risk of having incorrect information that can lead
to broken back/forward logic in apps.
It's also important that this state does not get modified by any logic in the
embedder process.  It should only be updated in response to navigation events in
the guest.  No assumptions should be made about how the index will change after
a navigation (e.g., for back, forward, or go), because the changes are not
always obvious.  For example, there is a maximum number of entries and earlier
ones will automatically be pruned.

[Fady Samuel, 2012/10/10 17:36:44]

Done.

   DISALLOW_COPY_AND_ASSIGN(BrowserPlugin);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_BROWSER_PLUGIN_BROWSER_PLUGIN_H_