Revert 157498 "Add an option to nextLinePosition to keep going a..."

It might have broken the following tests of interactive_ui_tests on Linux
Release, Linux Debug, Mac Release, and Windows Debug.

AutofillInteractiveTest.AutofillSelectViaTab
AutofillInteractiveTest.AutofillViaDownArrow
AutofillInteractiveTest.ComparePhoneNumbers
AutofillInteractiveTest.FormFillLatencyAfterSubmit
AutofillInteractiveTest.NoAutofillForReadOnlyFields

> Add an option to nextLinePosition to keep going and avoid getting stuck.
> 
> (Same to prevLinePosition.)
> Sometimes the logic used in nextLinePosition failed and it got stuck.
> One cause seemed to be when the next position it found ended up snapping
> back to the same visible position, depending on affinity. Explicitly
> overriding the affinity masked the problem in many cases, but didn't
> solve all cases and just caused other tests to break.
> 
> BUG=264769
> 
> Review URL: https://chromiumcodereview.appspot.com/20775002

TBR=dmazzoni@chromium.org
BUG=289136

Review URL: https://codereview.chromium.org/23783009

git-svn-id: svn://svn.chromium.org/blink/trunk@157566 bbb929c8-8fbe-4397-9dbb-9b2b20218538