constructor(width /*int*/, height /*int*/) {
			this.width = width;
			this.height = height;
			const bytes = new Array(height); // [height][width]
			for (let i = 0; i !== height; i++) {
				bytes[i] = new Uint8Array(width);
			}
			this.bytes = bytes;
		}
JAVAPORT: The original code was a 2D array of ints, but since it only ever gets assigned
-1, 0, and 1, I'm going to use less memory and go with bytes.

@author dswitkin@google.com (Daniel Switkin)