Re-land: Return an accessible value for all HTML input elements.
Re-land: Return an accessible value for all HTML input elements.

Original review: https://codereview.chromium.org/739753002/

This broke two content_browsertests, which have now been disabled
so they can be updated.

BUG=378799
TBR=aboxhall
NOTRY=true

Review URL: https://codereview.chromium.org/741093003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@185678 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs