Make `chrome` target build without unused data members on Linux.

extensions/browser/user_script_loader.h

Index: extensions/browser/user_script_loader.h
diff --git a/extensions/browser/user_script_loader.h b/extensions/browser/user_script_loader.h
index 80b13d68db0d0ba8d2810c344a1208dbce0b38c6..ff6772aa9b09dac37d3917960f75b3e73e166c60 100644
--- a/extensions/browser/user_script_loader.h
+++ b/extensions/browser/user_script_loader.h
@@ -165,9 +165,6 @@ class UserScriptLoader : public content::NotificationObserver {
   // finishes.  This boolean tracks whether another load is pending.
   bool pending_load_;
 
-  // Whether or not we are currently loading.
-  bool is_loading_;
-
   // The browser_context for which the scripts managed here are installed.
   content::BrowserContext* browser_context_;