alloc profile: record string allocs

[vilterp]

This calls directly into gc_pool_alloc, so we were missing it. Knocks a couple percentage points off of the missed alloc percentage.

[NHDaly]

Wanna maybe add a unit test that we catch strings like we expect?

[NHDaly]

Great catch, btw 👍

[NHDaly]

Maybe something like this?:

julia> Profile.Allocs.clear()

julia> Profile.Allocs.@profile sample_rate=1 "$(rand())"
"0.46487797515442597"

julia> p = Profile.Allocs.fetch()
Profile.Allocs.AllocResults(Profile.Allocs.Alloc[Profile.Allocs.Alloc(Vector{UInt8}, Base.StackTraces.StackFrame[unsafe_wrap at string.jl:85 [inlined], ...], 48)])

julia> @test length(p.allocs) >= 1
Test Passed
  Expression: length(p.allocs) >= 1
   Evaluated: 1 >= 1

julia> @test length([a for a in p.allocs if a.type == String]) >= 1
Test Failed at REPL[42]:1
  Expression: length([a for a = p.allocs if a.type == String]) >= 1
   Evaluated: 0 >= 1
ERROR: There was an error during testing

^ which failed for me, since i don't have this PR merged yet 😊

(The one allocation I did have was a Vector{UInt8}, i guess in the string(::Float64) method)

[vilterp]

Yep, good idea! Added your test; passes on this branch.