Light-weight stats counters for experiments.

Light-weight stats counters for temporary experiments/debugging.
A single statement is enough to add a counter:
  ...
  Isolate::Current()->counters()->Increment("allocated", size_in_bytes);
  ...

I've been using these myself for a while now, but figured others might
find them useful too. They are not intended for production use, just temporary local experiments/investigation.

R=johnmccutchan@google.com

Committed: https://code.google.com/p/dart/source/detail?r=37367

[Cutch, 2014-06-13 19:49:37]

lgtm and looks useful.

[Ivan Posva, 2014-06-13 22:14:32]

DBC -ip

https://codereview.chromium.org/336683003/diff/40001/runtime/vm/counters.cc
File runtime/vm/counters.cc (right):

https://codereview.chromium.org/336683003/diff/40001/runtime/vm/counters.cc#n...
runtime/vm/counters.cc:8: #include <map>
Please add a TODO to remove this.

[koda, 2014-06-16 17:12:48]

https://codereview.chromium.org/336683003/diff/40001/runtime/vm/counters.cc
File runtime/vm/counters.cc (right):

https://codereview.chromium.org/336683003/diff/40001/runtime/vm/counters.cc#n...
runtime/vm/counters.cc:8: #include <map>
On 2014/06/13 22:14:32, Ivan Posva wrote:
> Please add a TODO to remove this.

Done.

[koda, 2014-06-16 17:13:27]

Committed patchset #3 manually as r37367 (presubmit successful).