Consider merging https://chromium.googlesource.com/chromium/blink/+/dc0367e0c01205a6c9289e35260ca46ae4f86566 We never used AccessibilityRenderObject::previousSibling, and I've been scared for a long time someone would accidentally use it and we'd discover it's full of bugs, since it had no test coverage. (Several bugs have been caught in nextSibling over the years.) Time for it to die. We also don't need AccessibilityObject::lastChild, though the implementation was trivial. The public interface needs even less - we can get rid of firstChild, lastChild, nextSibling, and previousSibling, because childAt is the only one called.
good idea
<rdar://problem/16014110>