[Reland] Add a scrolling test for find-in-page

Turning on root-layer-scrolling caused find in page to break in Android
but wasn't turned up by tests. This CL adds a test to fill the gap. The
regression was incidentally fixed in r535827.

Also update TextFinder to use AbsoluteToRootFrame rather than
ContentsToRootFrame. The two are equivalent but I'd like to eventually
remove the Contents nomenclature since it can be easily confused for
being relative to the document origin.

This CL has no functional changes.

[Reland Note] Fixes unreachable code build failure.

TBR=treib@chromium.org,skobes@chromium.org,paulmeyer@chromium.org

Bug: 810067
Change-Id: Iee35b2e5ef27c4a8985080b6962108f64b947a17
Reviewed-on: https://chromium-review.googlesource.com/915786
Reviewed-by: David Bokan <bokan@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536403}
3 files changed