Please merge into dev channel

[johnmccutchan]

@whesse @mit-mit @kasperl

Part of dart:developer isn't ready for primetime in 1.13 and I want to make it private.

The following CL is against our dev branch as of this morning:

https://codereview.chromium.org/1430983003

[whesse]

Merged in 1.13.0-dev.7.10