Share one safeSelf() cache between the scriptlets in a frame

[philipp-classen]

Context: Each scriptlet has its own copy of safeSelf(). It saves the functions that it finds when it first runs, and those were often already the wrappers that earlier scriptlets had installed, not the browser's own functions. So each hook called all earlier hooks again. With six hooks on JSON.stringify (as on youtube.com), one JSON.stringify call from the page became 2^6=64 native calls.

The extension gives each scriptlet its own copy of scriptletGlobals, so the first scriptlet in a frame (and world) now keeps the cache on globalThis, and the later scriptlets use it. The property is read-only, and its key has the uBO version, so other versions do not share it. This works for all injection paths (registered scripts and executeScript), without changes in the extension.

refs ghostery/ghostery-extension#3672

[smalluban]

Why not something like this?

if (scriptletGlobals["safe-${tagName}"]) { 
  safeSelf.safe = scripletGlobals["safe-${tagName}"];
} else {
  scriptletGlobals["safe-${tagName}"] = safeSelf();
}

[smalluban]

The args are serialized and copied, so we cannot use scripletGlobals - it is meant to keep some configuration options.