I don't know why ready formats where skipped, but the WebGL specification states that the only valid types for gl.readPixels is RGBA and UNSIGNED_BYTE. And so haveing IMPLEMENTATION_COLOR_READ_FORMAT and IMPLEMENTATION_COLOR_READ_TYPE would not give you information you could use.
PACK_IMAGE_HEIGHT and PACK_SKIP_IMAGES are not part of OpenGL ES 2.0 (they're in ES 3.0) and since WebGL is an implementation of ES 2.0, they're not there (and they will not work in WebGL).
DRAW_BINDING is not in any specification I could find (it's not in ES 2.0, ES 3.0, ES 3.1, GL 2.0, GL 3.0 or GL 4.0). What's that parameter?