Improve accessible name calculation on Windows.

content/test/data/accessibility/button-name-calc-expected-win.txt

+ROLE_SYSTEM_DOCUMENT name='' READONLY FOCUSABLE description=''
+    IA2_ROLE_SECTION name='' READONLY description=''
+        ROLE_SYSTEM_PUSHBUTTON name='InnerText' FOCUSABLE description=''
+        ROLE_SYSTEM_PUSHBUTTON name='InnerText' FOCUSABLE description='Title'

[aboxhall, 2012/08/01 01:56:57]

Is using the title as the description the de facto standard? It's not mentioned
in the spec: "An accessible description may be computed by concatenating the
text alternatives for nodes referenced by an aria-describedby attribute on the
current node."

[dmazzoni, 2012/08/01 03:22:41]

I was following: http://www.w3.org/TR/html-aapi/#calc

For example: "If the control has a non-empty associated label element and a
non-empty title attribute, use the content of the associated label element as
the control's accessible name. Use the content of the title attribute as the
control's accessible description."

The way I'm interpreting it, the title is the primary text alternative, and if
there's a 2nd-priority text alternative string, it goes in the description,
UNLESS you use aria-describedby, which overrides the description.

[aboxhall, 2012/08/06 01:55:49]

Right, now I understand; I hadn't seen that spec before.

Annoyingly, the spec is kind of ambiguous as to what to do with aria-describedby
in the case where there is no aria-label or aria-labelledby, but I think your
approach is reasonable; i.e. aria-describedby overrides any other attributes. I
notice there is a "to do" under "Accessible Description Calculation", too.

+        ROLE_SYSTEM_PUSHBUTTON name='AriaLabel' FOCUSABLE description='Title'
+        ROLE_SYSTEM_PUSHBUTTON name='LabelledBy' FOCUSABLE description='Title'
+        ROLE_SYSTEM_PUSHBUTTON name='LabelledBy' FOCUSABLE description='DescribedBy'
+        ROLE_SYSTEM_PUSHBUTTON name='InnerText' FOCUSABLE description='DescribedBy'