Prerendered tabs use the same SessionStorage namespace as the tab that triggered the prerender.

content/browser/renderer_host/render_view_host.h

Index: content/browser/renderer_host/render_view_host.h
diff --git a/content/browser/renderer_host/render_view_host.h b/content/browser/renderer_host/render_view_host.h
index cb72b6cb8abc9cb51f3378f8b6c41b82123085ed..37720ffb5d1d7058ce73d65775397ce660951445 100644
--- a/content/browser/renderer_host/render_view_host.h
+++ b/content/browser/renderer_host/render_view_host.h
@@ -472,6 +472,10 @@ class CONTENT_EXPORT RenderViewHost : public RenderWidgetHost {
   // (and what action to take regarding the selection).
   void StopFinding(const ViewMsg_StopFinding_Params& params);
 
+  SessionStorageNamespace* session_storage_namespace() {
+    return session_storage_namespace_.get();
+  }
+
   // NOTE: Do not add functions that just send an IPC message that are called in
   // one or two places.  Have the caller send the IPC message directly.