Move IA2 State handling to AXPlatformNodeWin.

This CL moves all ia2_state handling from BrowserAccessibilityComWin to
AXPlatformNodeWin. In addition, we now forward get_states() to
AXPlatformNodeWin as well.

BUG=703369

Review-Url: https://codereview.chromium.org/2968833002
Cr-Commit-Position: refs/heads/master@{#485862}
7 files changed