Fix various issues seen in onScrollPositionChanged

onScrollPosition changed:
- accesses |Output| without setting any speech or braille to output. This causes access of a substring to return undefined and subsequently, a call to toString on an undefined object.
- onScrollPositionChanged does not respect ChromeVox mode (so likely will draw active indicator when the event gets fired after compat/classic mode switch which sets a ChromeVox range)
- it accesses state/location/boundsForRange on objects like webArea that seem to return undefined by the automation API. This violates our externs, so always get the externs to align with their actual usage. State is always defined, the others are sometimes undefined.

TEST=manual
BUG=581161

Review URL: https://codereview.chromium.org/1632093002

Cr-Commit-Position: refs/heads/master@{#373671}

0 files changed, 0 insertions, 0 deletions