The pprof tool utilizes attributes of mapping entries
such as HasFunctions to determine whether the profile
includes necessary symbol information.
If none of the attributes is set, pprof tool tries to
read the corresponding binary to use for local symbolization.
If the binary doesn't exist, it prints out error messages.

Go runtime generated profiles without any of the attributes
set so the pprof tool always printed out the error messages.
The error messages became more obvious with the new
terminal support that uses red color for error messages.

Go runtime can symbolize all Go symbols and generate
self-contained profile for pure Go program. Thus, there
is no reason for the pprof tool to look for the copy of
the binary. So, this CL sets one of the attributes
(HasFunctions) true if all PCs in samples look fully
symbolized.

For non-pure Go program, however, it's possible that
symbolization of non-Go PCs is incomplete. In this case,
we need to leave the attributes all false so pprof can attempt
to symbolize using the local copy of the binary if available.
It's hard to determine whether a mapping includes non-Go
code. Instead, this CL checks PCs from collected samples.
If unsuccessful symbolization is observed, it skips setting
the HasFunctions attribute.

Fixes #25743

Change-Id: I5108be45bbc37ab486d145fa03e7ce37d88fad50
Reviewed-on: https://go-review.googlesource.com/118275
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>