Bind listener to keyup to capture arrows & better math for scrolling.

Listen to keyup to properly capture and respond to up and down arrows.
Rewrite calculation for scroll to better follow toolbar obscured cursor.

Bug: 48787
Change-Id: Ia46fb15ec9a8c07b3945b53a6545897ca23e59fa
Merge "Bind listener to keyup to capture arrows & better math for scrolling."