Add structs to WebViewImpl to hold members.

One struct holds things that will stay in the eventual WebViewImpl, and
the other holds things that will move to WebWidgetImpl once they are
split.

This will allow us to DCHECK that you're not inside a WebWidget API call
when you access ViewData, or vice versa. And it makes users clear within
the WebViewImpl class which one they are acting on, as we make a
decision where each variable belongs. It also allows us to do that
incrementally.

R=dcheng@chromium.org

Change-Id: I255cf0de838928e3f88c805563017702067e0d48
Bug: 912193
Reviewed-on: https://chromium-review.googlesource.com/c/1388920
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#618666}
3 files changed