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

extensions/common/extension_messages.h

Index: extensions/common/extension_messages.h
diff --git a/extensions/common/extension_messages.h b/extensions/common/extension_messages.h
index 232167c224f15ec3eb77cb540d14c65a7d9a542c..ac7f5758da7e6ff89b04300e71e2d1a6eba23e27 100644
--- a/extensions/common/extension_messages.h
+++ b/extensions/common/extension_messages.h
@@ -450,16 +450,17 @@ IPC_MESSAGE_ROUTED1(ExtensionMsg_ExecuteCode,
 // 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,