Coverage is calculated as
exe / (inst + miss). In general, lines that are in
miss should be ignored, but our exclusion rules are not good enough.
Buildbots are currently on the experimental waterfall. The coverage figures they calculate come from running some subset of the chromium testing suite.
Sometimes a line of code should never be reached (e.g.,
NOTREACHED()). These can be marked in the source with
// COV_NF_LINE. Note that this syntax is exact.