Re-land: Adding PreRole in blink side to expose HTML pre tag with correct MSAA+IA2.

It was reverted due to bug 426608; the fix was landed on the Chromium side.

Original review url: https://codereview.chromium.org/671003002

BUG=426608,426053
TBR=leviw

Review URL: https://codereview.chromium.org/663233004

git-svn-id: svn://svn.chromium.org/blink/trunk@184337 bbb929c8-8fbe-4397-9dbb-9b2b20218538