Mac: Fix tab view accessibility.
The close button was setting the AXDescription property, it somehow caused
VoiceOver to use it as the tab view's description. Change it to set the AXTitle
property instead to fix the issue, and to match Safari.
Also change the tab strips' AX children to be sorted from left to right, so
that VoiceOver's "Tab X of Y" order is always ascending left to right.
BUG=415570
Review URL: https://codereview.chromium.org/
588393002
Cr-Commit-Position: refs/heads/master@{#296346}