dashboard: separate build and non-build metrics in perf dashboard As per Ian request:
dashboard: separate build and non-build metrics in perf dashboard
As per Ian request:

>> Let's clearly separate the build numbers from the runtime numbers.
>> The build numbers are interesting but there are many things that
>> affect them.  The runtime numbers are presumably stable.

LGTM=adg
R=adg
CC=golang-codereviews, iant, rsc
https://golang.org/cl/154440043

evandbrown/build,golang/build,proppy/build,golang/build,proppy/build,golang/build,evandbrown/build,proppy/build,evandbrown/build,proppy/build,golang/build