[whatwg] Proposing <canvas>.toBlob(contentType)

[Kyle Huey]

Hello All,

Gecko 2.0 ships with a non-standard method on <canvas> named
mozGetAsFile(contentType, fileName).  We added this for internal use in our
UI.  It retrieves the contents of the canvas as a File object (at the time
Gecko did not supports Blobs) encoded in the contentType according to the
same rules toDataURL uses.

I propose adding a toBlob(contentType) method to the canvas element in the
style of toDataURL.  This would greatly increase the options available to
developers for extracting data from a canvas element (a Blob can be saved to
disk, XHRed, etc.)

- Kyle