Minor code-style tweaks in `lib/typechecker.dart` using the formatter. I mainly run the tool, but I added a couple extra things either to comply with our style or to help the formatter. I filed bugs for the cases were the formatter didn't do what I expected.
Minor code-style tweaks in `lib/typechecker.dart` using the formatter. I mainly
run the tool, but I added a couple extra things either to comply with our style
or to help the formatter. I filed bugs for the cases were the formatter didn't
do what I expected.

BUG=
R=vsm@google.com

Review URL: https://chromereviews.googleplex.com/117277013

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