style(trackable_value): change WatchableValueInterface to use ReadonlyNullarySignal
style(trackable_value): change WatchableValueInterface to use ReadonlyNullarySignal

janelia-flyem/neuroglancer,seung-lab/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,google/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,janelia-flyem/neuroglancer,seung-lab/neuroglancer,seung-lab/neuroglancer,seung-lab/neuroglancer,google/neuroglancer,seung-lab/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,seung-lab/neuroglancer,google/neuroglancer,seung-lab/neuroglancer,google/neuroglancer