Forward BrowserAccessibility get_accState to AXPlatformNode.

This is another migration from BrowserAccessibility to AXPlatformNodeWin.
In this installment, we're converting get_accState.

We attempted to land this CL in https://codereview.chromium.org/2913553002/.
The CL was reverted due to lack of adequate testing. We since have improved
our testing in bug 733437.

BUG=703369

Review-Url: https://codereview.chromium.org/2943243002
Cr-Commit-Position: refs/heads/master@{#482751}
14 files changed