Merge services into a shared IOService in dart:io, and use a native port.

Merge services into a shared IOService in dart:io, and use a native port.

BUG=
R=sgjesse@google.com

Committed: https://code.google.com/p/dart/source/detail?r=27883

[Søren Gjesse, 2013-09-25 08:49:03]

Please go ahead with this change. However as long as there is not thread pool
for the native isolates we still need to do some multiplexing in the IO service.

[Anders Johnsen, 2013-09-25 14:02:14]

PTAL, done porting all the services. There is now only 32 shared ports.

[Søren Gjesse, 2013-09-25 14:55:53]

LGTM, nice cleanup

[Anders Johnsen, 2013-09-25 15:03:59]

Committed patchset #4 manually as r27883 (presubmit successful).