<script src="..." is very dangerous. At best, you can vet the src and check to see if it's benign or not. Often times, that vendor and their "1-line of javascript to get our whiz-bang service" in turn loads other javascript files. I don't see how cryptographically signing the bootloader solves anything in this case. Compromised analytics or vendor javascript will still lead to total site pwnage if I'm reading this right.