Draft CL: https://chromium-review.googlesource.com/c/602606/

To resolve  Issue 692856 , this issue tracks efforts to introduce
ScriptResourceData.
ScriptResource represents everything needed by the users of ScriptResource after loading finished, that is, almost everything needed by the users of ScriptResource except for ScriptStreamer.
On load finish, ScriptResourceData is created (contains Request URL, ResourceResponse, SharedBuffer/String, etc.) and all other classes refer to ScriptResourceData, instead of ScriptResource directly.
By doing so, revalidation of ScriptResource no longer affects ScriptResourceClients that are already notified of finish, because revalidation modifies ScriptResource, but doesn't modify the existing ScriptResourceData. In this way, this fixes  Issue 692856 .

Design doc to be written.