[ios] Pass Browser* instead of ProfileIOS* to LoadJavaScriptURL(...)

In preparation of converting PrerenderService to a Browser agent,
change LoadJavaScriptURL(...) to take the Browser* instead of the
ProfileIOS*.

Bug: 40726702
Change-Id: I7df6911b7fbb026b4f69badb518198f7622f5ad7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6850509
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Quentin Pubert <qpubert@google.com>
Cr-Commit-Position: refs/heads/main@{#1505783}