a11y: Exclude children of nested keyboard accessible controls from a11y tree.
Currently, children of keyboard accessible controls, such as the Labels inside
LabelButtons, are not hidden from the accessibility tree. This is not useful
because the user only cares about the element that has focus, not any children
inside it, which are implementation details. Set any children of keyboard
accessible controls to have ignored roles, which indicates to the OS (works for
Windows, Mac, and Linux) that the ignored element should be excluded from the
accessibility tree.
BUG=610589,723574
TEST=On Mac: Open the XCode Accessibility Inspector. On Windows: Open the
Windows SDK 'Inspect.exe' and make sure the icon for 'Watch Focus' is selected.
Then (on Mac, hover over; on Windows, focus) a views::LabelButton (e.g. on the
HTTP Authentication dialog). It should report an empty set of children and its
role ("Type"/"accessibilityRole" on Mac; "Role"/"ControlType" on Windows) should
say it is a button.
Review-Url: https://codereview.chromium.org/2119413004
Cr-Commit-Position: refs/heads/master@{#474867}
7 files changed
