parseAvailability( subtree, subtreeJson, bufferViewsU8 ) {

		const branchingFactor = getBoundsDivider( this.rootTile );
		const subtreeLevels = this.rootTile.implicitTiling.subtreeLevels;
		const tileAvailabilityBits =
			( Math.pow( branchingFactor, subtreeLevels ) - 1 ) / ( branchingFactor - 1 );
		const childSubtreeBits = Math.pow( branchingFactor, subtreeLevels );
		subtree._tileAvailability = this.parseAvailabilityBitstream(
			subtreeJson.tileAvailability,
			bufferViewsU8,
			tileAvailabilityBits
		);
		subtree._contentAvailabilityBitstreams = [];
		for ( let i = 0; i < subtreeJson.contentAvailabilityHeaders.length; i ++ ) {

			const bitstream = this.parseAvailabilityBitstream(
				subtreeJson.contentAvailabilityHeaders[ i ],
				bufferViewsU8,
				// content availability has the same length as tile availability.
				tileAvailabilityBits
			);
			subtree._contentAvailabilityBitstreams.push( bitstream );

		}
		subtree._childSubtreeAvailability = this.parseAvailabilityBitstream(
			subtreeJson.childSubtreeAvailability,
			bufferViewsU8,
			childSubtreeBits
		);

	}
Parse the three availability bitstreams and store them in the subtree.

@param {Subtree} subtree The subtree to modify.
@param {Object} subtreeJson The subtree JSON.
@param {Object} bufferViewsU8 A dictionary of buffer view index to a Uint8Array of its contents.
@private