Android accessible hint text should include placeholder.

Previously a text field's placeholder was exposed as the
hint in many circumstances, but a field that had
aria-describedby would override the placeholder.

Update the logic so that the placeholder text is
always included in the hint text for a node.

Bug: 677147
Change-Id: I15c7cfede914db6096d88039213793ec2eaa8ad4
Reviewed-on: https://chromium-review.googlesource.com/c/1385724
Commit-Queue: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#622150}
7 files changed