1) Turn on whole file context

2) Go to https://chromium-review.googlesource.com/c/517867/16/cc/trees/layer_tree_host_common_unittest.cc#9519

3) Try to add a comment.

It takes more than a second for each character to type, and like 10 seconds to even open the file. Rietveld wasn't the fastest on large files but this is much worse, it seems like there's some bad algorithmic complexity going on.