Move AsynchronousCloseMonitor to libjavacore.

Final resting place tbd (see b/122881655) but this gets
it out of libnativehelper.

Bug: 122881655
Test: m && flashall
Test: atest CtsLibcoreOkHttpTestCases:com.squareup.okhttp.CallTest

Change-Id: I4354dd90f2ce5fa18734974efd1b6bad49ec0307
7 files changed