runtime/pprof: spotty tests for several builders

[Luit]

Tests mostly pass, but fail sometimes. 

Seen on linux/arm (and android), linux/386, linux/amd64, and amd64 builds on solaris,
freebsd, dragonfly ...

Failure looks like this:

--- FAIL: TestGoroutineSwitch (0.48s)
    pprof_test.go:271: found profile entry for runtime.gogo:
        0x8078904 /usr/local/go/src/runtime/asm_386.s:155
        0x8058d10 /usr/local/go/src/runtime/proc.go:114
        0x80a1064 /linux-386-3e5d0270f09e/go/src/runtime/pprof/pprof_test.go:240
        0x8092fa1 /usr/local/go/src/testing/testing.go:448
FAIL
FAIL    runtime/pprof   7.214s


Examples:
builder linux-386: http://build.golang.org/log/33c4f62680b98e004a0fabbb68be5278e12e4d3a
builder linux-arm-luitvd:
http://build.golang.org/log/ddbcae0c6285b0fb59df48e9072adf24a3c75312
builder freebsd-amd64:
http://build.golang.org/log/acf42712fca1d6d87f7365e5d3270bd6053241b7

[ianlancetaylor]

Comment 1:

Labels changed: added repo-main, release-go1.4maybe.

[Luit]

Comment 2:

Revision 0a372305e9a1 seems to have fixed it for the consistently failing
linux-arm-luitvd builder, and no other buils have failed like this again so far.

[rsc]

Comment 3:

Status changed to Fixed.