We were using File.readAsBinaryString() to get the contents of an

uploaded file. While Chrome and Firefox support this still, it's

actually a deprecated function that never made it out of beta, and IE

doesn't support it.
The proper solution, which is a bit more lengthy, is to read in as an

ArrayBuffer, create a Uint8Array view around it, and then convert the

contents to characters in the payload. This works on all browsers.

Tested uploading a diff on IE 10, 11, Firefox, and Chrome.
Unit tests pass.
Tested uploading valid Git diffs, empty files, and non-diff text files.