Fix longstanding architectural issues

ext/src/cast/contentInitial.ts

@@ -0,0 +1,57 @@
+/**
+ * Content script loaded on whitelisted URLs. Sets some window
+ * properties to help with Chrome compatibility and handles dynamic
+ * chrome-extension:// cast script loads.
+ */
+
+import { CAST_LOADER_SCRIPT_URL, CAST_SCRIPT_URLS } from "./urls";
+
+declare global {
+    interface Object {
+        wrappedJSObject: this;
+    }
+
+    interface Window {
+        wrappedJSObject: Window;
+        chrome: {
+            cast?: object;
+        };
+        __onGCastApiAvailable: (isAvailable: boolean) => void;
+    }
+    interface Navigator {
+        presentation: object;
+    }
+}
+
+window.wrappedJSObject.chrome = cloneInto({}, window);
+
+/**
+ * YouTube won't load the cast SDK unless it thinks the presentation API
+ * exists.
+ */
+if (window.location.host === "www.youtube.com") {
+    window.wrappedJSObject.navigator.presentation = cloneInto({}, window);
+}
+
+const srcPropDesc = Reflect.getOwnPropertyDescriptor(
+    HTMLScriptElement.prototype.wrappedJSObject,
+    "src"
+);
+/**
+ * Intercept script element src attribute changes and rewrite cast
+ * script URLs to the remote loader script URL to be redirected by the
+ * extension's webRequest handlers in the background script.
+ */
+Reflect.defineProperty(HTMLScriptElement.prototype.wrappedJSObject, "src", {
+    configurable: true,
+    enumerable: true,
+    get: srcPropDesc?.get,
+
+    set: exportFunction(function (this: HTMLScriptElement, value: string) {
+        if (CAST_SCRIPT_URLS.includes(value)) {
+            return srcPropDesc?.set?.call(this, CAST_LOADER_SCRIPT_URL);
+        }
+
+        return srcPropDesc?.set?.call(this, value);
+    }, window)
+});