Move Page into the WebView portion of WebViewImpl.

Accessors of it grab it through AsView(). After this we will start to
add guards to prevent AsView() calls inside WebWidget API methods.

1st open question is if WebWidget APIs should be able to access the
main frame and if so if it should be through the WebView/Page or
elseways.

2nd open question is if WebView APIs using the Page should be allowed
to touch the frames (and frame views) at all.

R=dcheng@chromium.org

Change-Id: I141e5660d48ae5b3227aed8525e6f6999c6f6413
Bug: 912193
Reviewed-on: https://chromium-review.googlesource.com/c/1399742
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621292}
2 files changed