Reset RendererAccessibility state when enabling tree only accessibility mode.
When a caller of the automation extension API requests a tree (desktop or tabs) for a previously requested tree, a load complete does not fire as a result of the request. This is problematic when the caller was not the one to make any of the previous requests.
To reproduce:
- turn on ChromeVox in OOBE
- notice all elements are read
- toggle ChromeVox
- notice some elements are no longer read.
This is because ChromeVox attempts to call EnableFrame() on a subtree of the desktop tree. The request on the browser side attempts to enable tree only accessibility on a rfh that already has tree only accessibility enabled. The call returns early as a result. Events fired on this subtree never get handled inside of the extension because the tree data never got sent.
BUG=488693
Review URL: https://codereview.chromium.org/
1215063002
Cr-Commit-Position: refs/heads/master@{#339051}