Tests that long data: URLs are correctly trimmed in MIME type console warnings.

Bug 100083
script-as-text-loading-data-url.html:10 Resource interpreted as Script but transferred with MIME type text/plain: "data:text/plain;base64,dmFyIGpvaG5xdW90ZSA9ICJCZWNhdXNlIG9mIHRoZSBuYXR1cmUg…JlbHkgY29tcGV0ZW50IHByb2dyYW1tZXIgc29tZSBudW1iZXIgb2YgeWVhcnMgbGF0ZXIuIjs=".