Abstract content::SessionStorageNamespace from core TabRestore code

components/sessions/core/tab_restore_service_client.h

Index: components/sessions/core/tab_restore_service_client.h
diff --git a/components/sessions/core/tab_restore_service_client.h b/components/sessions/core/tab_restore_service_client.h
index 99f1089c08adb12aa109f7944f18e23b8bdd2424..121cf509c7ea90ae875c8504fd06c8ec162de53c 100644
--- a/components/sessions/core/tab_restore_service_client.h
+++ b/components/sessions/core/tab_restore_service_client.h
@@ -7,8 +7,10 @@
 
 #include "base/callback.h"
 #include "base/files/file_path.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/scoped_vector.h"
 #include "components/sessions/session_id.h"
+#include "components/sessions/sessions_export.h"
 
 namespace base {
 class CancelableTaskTracker;
@@ -37,9 +39,19 @@ struct SessionWindow;
 typedef base::Callback<void(ScopedVector<SessionWindow>, SessionID::id_type)>
     GetLastSessionCallback;
 
+// A class that is used to associate embedder-specific data with
+// TabRestoreService::Tab. See TabRestoreServiceClient::GetClientData().
+class SESSIONS_EXPORT TabClientData : public base::RefCounted<TabClientData> {

[blundell, 2015/09/15 19:38:57]

Note that this class needs to be refcounted because the Tab struct is copied and
assigned all over the place (I should probably put a comment to that effect in
the code...).

[sky, 2015/09/15 21:59:49]

I hate to propagate that. How about a Clone() method on TabClientData?

[blundell, 2015/09/16 11:53:51]

Done.

+ protected:
+  virtual ~TabClientData() {}
+
+ private:
+  friend class base::RefCounted<TabClientData>;
+};
+
 // A client interface that needs to be supplied to the tab restore service by
 // the embedder.
-class TabRestoreServiceClient {
+class SESSIONS_EXPORT TabRestoreServiceClient {
  public:
   virtual ~TabRestoreServiceClient() {}
 
@@ -81,6 +93,12 @@ class TabRestoreServiceClient {
   virtual std::string GetExtensionAppIDForWebContents(
       content::WebContents* web_contents) = 0;
 
+  // Returns any client data that should be associated with the
+  // TabRestoreService::Tab corresponding to |web_contents|. That tab will own
+  // this reference to the returned data.
+  virtual scoped_refptr<TabClientData> GetTabClientDataForWebContents(
+      content::WebContents* web_contents) = 0;
+
   // Get the sequenced worker pool for running tasks on the backend thread as
   // long as the system is not shutting down.
   virtual base::SequencedWorkerPool* GetBlockingPool() = 0;