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 a295822b04dc0890e6d2f166d2e5fd19716d3dcc..0f12390468a2e2990236207dde4deb05d3bef9ff 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.