Refactoring: de-couple Extensions from "script injection System" [render side]:4

extensions/common/extension_messages.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // IPC messages for extensions.
 // Multiply-included message file, hence no include guard.
 
 #include <string>
 #include <vector>
 
@@ skipping 432 matching lines @@
 
 // Notification that renderer should run some JavaScript code.
 IPC_MESSAGE_ROUTED1(ExtensionMsg_ExecuteCode,
                     ExtensionMsg_ExecuteCode_Params)
 
 // Notification that the user scripts have been updated. It has one
 // SharedMemoryHandle argument consisting of the pickled script data. This
 // handle is valid in the context of the renderer.
 // If |owner| is not empty, then the shared memory handle refers to |owner|'s
 // programmatically-defined scripts. Otherwise, the handle refers to all
-// extensions' statically defined scripts.
-// If |changed_extensions| is not empty, only the extensions in that set will
-// be updated. Otherwise, all extensions that have scripts in the shared memory
-// region will be updated. Note that the empty set => all extensions case is not
+// hosts' statically defined scripts. So far, only extension-hosts support
+// statically defined scripts; WebUI-hosts don't.
+// If |changed_hosts| is not empty, only the host in that set will
+// be updated. Otherwise, all hosts that have scripts in the shared memory
+// region will be updated. Note that the empty set => all hosts case is not
 // supported for per-extension programmatically-defined script regions; in such
-// regions, the owner is expected to list itself as the only changed extension.
+// regions, the owner is expected to list itself as the only changed host.
 IPC_MESSAGE_CONTROL3(ExtensionMsg_UpdateUserScripts,
                      base::SharedMemoryHandle,
-                     extensions::ExtensionId /* owner */,
-                     std::set<std::string> /* changed extensions */)
+                     HostID /* owner */,
+                     std::set<HostID> /* changed hosts */)
 
 // Trigger to execute declarative content script under browser control.
 IPC_MESSAGE_ROUTED4(ExtensionMsg_ExecuteDeclarativeScript,
                     int /* tab identifier */,
                     extensions::ExtensionId /* extension identifier */,
                     int /* script identifier */,
                     GURL /* page URL where script should be injected */)
 
 // Tell the render view which browser window it's being attached to.
 IPC_MESSAGE_ROUTED1(ExtensionMsg_UpdateBrowserWindowId,
@@ skipping 312 matching lines @@
                     int /* acc_obj_id */,
                     base::string16 /* selector */)
 
 // Result of a query selector request.
 // result_acc_obj_id is the accessibility tree ID of the result element; 0
 // indicates no result.
 IPC_MESSAGE_ROUTED3(ExtensionHostMsg_AutomationQuerySelector_Result,
                     int /* request_id */,
                     ExtensionHostMsg_AutomationQuerySelector_Error /* error */,
                     int /* result_acc_obj_id */)