AX nodes that aren't contenteditable should be readonly.

We were returning the wrong result from AXObjects that
did not descend from AXNodeObject.

BUG=471075

Review URL: https://codereview.chromium.org/1039023002

git-svn-id: svn://svn.chromium.org/blink/trunk@192906 bbb929c8-8fbe-4397-9dbb-9b2b20218538
5 files changed