Browser Plugin: Implement CanGoBack/CanGoForward

content/renderer/browser_plugin/browser_plugin.h

Index: content/renderer/browser_plugin/browser_plugin.h
diff --git a/content/renderer/browser_plugin/browser_plugin.h b/content/renderer/browser_plugin/browser_plugin.h
index 45ae96d09a691c0183cc628fcfa455306bd19031..49a620e8fecb3c9d71aa27575f618e9d4c121e62 100644
--- a/content/renderer/browser_plugin/browser_plugin.h
+++ b/content/renderer/browser_plugin/browser_plugin.h
@@ -40,6 +40,10 @@ class CONTENT_EXPORT BrowserPlugin :
   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.
@@ -54,6 +58,8 @@ class CONTENT_EXPORT BrowserPlugin :
   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.
@@ -200,6 +206,8 @@ class CONTENT_EXPORT BrowserPlugin :
 #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);
 };