Adds new frame-level service with one initial method to handle host zoom
level.
This moves zoom level supply from async_resource_handler.cc to being a
request made when render_frame_impl handles a willSendRequest.
The goal of this change is to remove the dependency of
content/browser/loader on the rest of content/browser in particular
here, removing the use of c/b/host_zoom_map_impl.h in
content/browser/loader/async_resource_handler.cc.
BUG=598073,609607
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_site_isolation
Review-Url: https://codereview.chromium.org/1964273002
Cr-Original-Commit-Position: refs/heads/master@{#394547}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 68c6f2ce16d9807b5cb82679099c82c40f39e911
c059bd24e5