Add delegate method to allow accessing index_in_parent from AXNode.

Currently BrowserAcccessibility has a AXNode* that it uses to calculate
the hypertext offsets from child.  When we move this functionality to
AXPlatformNode, we'll want to be able to access the index_in_parent
from the AXNodeData.

Bug: 703369
Change-Id: I8db027e32c47b1ae55cb640d6aa00907fe57381a
Reviewed-on: https://chromium-review.googlesource.com/638445
Commit-Queue: Doug Turner <dougt@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#499551}
10 files changed