Make the MR dialog issue banner readable by screen readers

This CL makes the text in issue banners selectable by pressing tab, which allows
screen readers to read the text. This CL also adds aria-live attribute to the
text, but it is currently not functional.

BUG=651277

CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2267253002
Cr-Commit-Position: refs/heads/master@{#436510}
1 file changed