Added unit testing support.

Add lock to shutdown_fd() callback in udp_server.c

Hybrid CQ support

Avoid duplication in Bazel rules by using grpc_cc_libraries rule-creator

Fix semantics of LB policy selection.

Fix HTTP proxy tests

Demote handshake logging msg to DEBUG

Track calls to gpr_now()

C++ compatibility fix for tmpfile_posix.c

C++ compatibility fix for stack_lockfree.c

- heap allocate the pollset shutdown closure (this may be called asynchronously)
- ensure a poller remains until all endpoints are closed

Move response message processing to a user-specified queue

Fix and test Bazel build rules

Fix http2_interop test for c++ and python

Change slice_hash_table to use linear probing and add unit test.

Fix Error Refcount Bug

Extend time capping to run_tests_matrix scripts