Rework some UserScriptLoader logic in preparation to removing UserScript copy.

extensions/common/user_script.cc

Index: extensions/common/user_script.cc
diff --git a/extensions/common/user_script.cc b/extensions/common/user_script.cc
index 20bff9f159c4b8954ef39c50a1254367d787030c..ddf1fb39c0545226441ebdcd0809d996483d004f 100644
--- a/extensions/common/user_script.cc
+++ b/extensions/common/user_script.cc
@@ -288,6 +288,15 @@ void UserScript::UnpickleScripts(const base::Pickle& pickle,
   }
 }
 
+UserScriptIDPair::UserScriptIDPair(int id, const HostID& host_id)
+    : id(id), host_id(host_id) {}
+
+UserScriptIDPair::UserScriptIDPair(int id) : id(id), host_id(HostID()) {}
+
+bool operator<(const UserScriptIDPair& a, const UserScriptIDPair& b) {
+  return a.id < b.id;
+}
+
 bool operator<(const UserScript& script1, const UserScript& script2) {
   // The only kind of script that should be compared is the kind that has its
   // IDs initialized to a meaningful value.