GitLab

This CL fixes two issues.
. It brings up a scroll bar if the text in the feedback window doesn't fit in
  the space available on screen (this happens when the user sets the page zoom
  too 120% or above)
. Sets the focus to the description field when the feedback app starts.

R=xiyuan@chromium.org
BUG=295999,330139

Review URL: https://codereview.chromium.org/511393002

Cr-Commit-Position: refs/heads/master@{#292530}