Bug 966591 - Part 1: Put very basic hit region interface in + add runtime flag. r=roc
Bug 966591 - Part 2: Validate input to AddHitRegion. Provide partial implementation. r=roc
Bug 966591 - Part 3: Compute bounds of current path and set them as the accessible region. r=roc
Bug 966591 - Part 4: Complete implementation of removeHitRegion. r=roc
Bug 966591 - Part 5: Pass hit bounds to a11y code. r=surkov
Bug 966591 - Part 6: Some bug fixes to match spec. r=roc
Bug 966591 - Part 7: Bounds + error handling tests. r=surkov