These properties are not used from either JS or C++, and hence can be removed from both nsITreeBoxObject and TreeBoxObject.webidl. Properties in this bucket: scrollToCell, scrollToColumn, scrollToHorizontalPosition, invalidateColumnRange.

These properties are unused from C++ and the FakeTreeBoxObject implementations in comm-central are throwing stubs. So it's safe to remove the properties from nsITreeBoxObject (but not TreeBoxObject.webidl, since they're used in JS). Properties in this bucket: horizontalPosition, getPageLength.

These properties are unused from C++ apart from webidl bindings and the FakeTreeBoxObject implentations in comm-central are throwing stubs. But they're used in JS. They are safe to remove from nsITreeBoxObject but we need to keep an implementation webidl can call into. Properties in this bucket: selectionRegion, ensureCellIsVisible, scrollToRow, scrollByLines, scrollByPages, getRowAt, removeImageCacheEntry.

Pushed by bzbarsky@mozilla.com: https://hg.mozilla.org/integration/mozilla-inbound/rev/5b8e7ac3a4a5 part 1. Remove some unused tree box object properties. r=mossop https://hg.mozilla.org/integration/mozilla-inbound/rev/99016a1b4105 part 2. Remove some nsITreeBoxObject properties that are unused from C++. r=mossop https://hg.mozilla.org/integration/mozilla-inbound/rev/ada451d2e78d part 3. Remove some nsITreeBoxObject properties that are unused except via webidl bindings. r=mossop

https://hg.mozilla.org/mozilla-central/rev/5b8e7ac3a4a5 https://hg.mozilla.org/mozilla-central/rev/99016a1b4105 https://hg.mozilla.org/mozilla-central/rev/ada451d2e78d