Spun off this review comment: https://codereview.chromium.org/2746713003/diff/1/third_party/WebKit/Source/bindings/tests/results/core/NodeOrLongSequenceOrEventOrXMLHttpRequestOrStringOrStringByteStringOrNodeListRecord.h

"IIUC this kind of too long file name is problematic on Windows
(crbug.com/611437). We have utilities.shorten_union_name() to work around the
problem.

I think we should check the length of a given union type and throw an exception
if it's too long (100 characters?) but doesn't have an alias."

I don't have access to issue 611437, but it seems to be yet another case of Windows causing headaches due to path size limitations.

Setting a maximum threshold for a union name should alleviate the pain, but it's not clear if utilities.shorten_union_name() should do that or if that check should be done somewhere else.