Mark all private functions in dart: libraries as invisible (*sniff*).

Mark all private functions in dart: libraries as invisible (*sniff*). Previously these functions were only marked invisible if they were also native, a constructor, or on a black list.

An invisible function is hidden from stack traces, will not be enumerated
by mirrors, and cannot be directly invoked by mirrors. Note that private
classes remain accessible.

Fix a few internal dart:io functions that should be private.

Fix bug where mirrors would enumerate top-level invisible functions.

Mark observatory test that was using such private functions through
mirrors as failing.

BUG=http://dartbug.com/15274
R=hausner@google.com

Committed: https://code.google.com/p/dart/source/detail?r=43019

[rmacnak, 2015-01-16 23:29:00]

rmacnak@google.com changed reviewers:
+ gbracha@google.com, hausner@google.com, johnmccutchan@google.com

[hausner, 2015-01-16 23:45:54]

LGTM

[rmacnak, 2015-01-20 18:32:37]

Committed patchset #2 (id:20001) manually as 43019 (presubmit successful).