Call ComputeWebKitPrefs on the correct RVH, and remove dead code.
RenderViewHost was calling out to WebContents to get the URL, but it
was getting the wrong URL (e.g., possibly the transient one) and then
never looking at it. Worse, WebContents then called ComputeWebkitPrefs
on the wrong RVH (the old one, not the pending one).
This only seems to come up in corner cases, like chrome://history on
Android when Javascript is disabled.
BUG=454063
TEST=See bug.
TBR=jam
Review URL: https://codereview.chromium.org/
919933002
Cr-Commit-Position: refs/heads/master@{#316081}