Merge FrameView and ScrollView.

BUG=417774

Review URL: https://codereview.chromium.org/641733004

git-svn-id: svn://svn.chromium.org/blink/trunk@183555 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Ensure that FrameLoadTypeBackForward only occurs once per navigation.

With this change, TypeBackForward will only occur once at the top level navigation, and sub-frames that are created along the way will get TypeInitialInChildFrame.

BUG=416184
TEST=as in bug

Review URL: https://codereview.chromium.org/640663003

git-svn-id: svn://svn.chromium.org/blink/trunk@183556 bbb929c8-8fbe-4397-9dbb-9b2b20218538