src/vs/workbench/api/common/extHostWebviewMessaging.ts/ArrayBufferSet/add
class ArrayBufferSet:	public add(buffer: ArrayBuffer): number {
		let index = this.buffers.indexOf(buffer);
		if (index < 0) {
			index = this.buffers.length;
			this.buffers.push(buffer);
		}
		return index;
	}