Make window.scroll properties relative to the layout viewport by default.

This CL sets the inert-visual-viewport flag to true by default. The following
APIs in the CSSOM spec are affected: scrollTo, scrollBy, innerWidth,
innerHeight, scrollX, scrollY, element.scrollTop, element.scrollLeft,
element.scrollIntoView.

Intent-to-ship:
https://groups.google.com/a/chromium.org/d/msg/blink-dev/mt1uciFuvWQ/ecQi0f8kCQAJ

BUG=489206

Review URL: https://codereview.chromium.org/1416283006

Cr-Commit-Position: refs/heads/master@{#358117}
10 files changed