This reverts commit 0cb7fef4.

Useful for situations where we need to repeatedly trylock, not useful
for cases where we need to lock (due to spinning).

Add a variant of sync_test to test it (with the same tests we run for
gpr_mu).

Add a benchmark to bm_closure to demonstrate single threaded performance.

Based on soltanmm-google's #9114

Allow Node tests to run with or without UV, change default version to 7, add some portability tests. Also make some more core tests work with libuv

This commit fixes an issue in which the following sequence of operations
leads to use of uninitialized memory:

1. Caller invokes GrpcBufferWriter::Next(), and then makes use of 8191
   bytes in the returned buffer (which is 8192 bytes in size).

2. Caller then returns the unused single byte via
   GrpcBufferWriter::BackUp(). This method invokes
   g_core_codegen_interface->grpc_slice_split_tail(), which causes
   backup_slice_ to be a grpc_slice with one byte.

3. At the next invocation of GrpcBufferWriter::Next(), a reference to
   the single byte grpc_slice is returned to the caller.

The problem here is that the returned reference is to the inlined buffer
in the grpc_slice, which is resident in slice_, not the location of the
buffer inside slice_buffer_ after
g_core_codegen_interface->grpc_slice_buffer_add() in
GrpcBufferWriter::Next(). As a result, any data the caller writes to the
returned void* data is lost.

The solution is to avoid inlined backup slices.

This PR adds a set of debug helpers that are intended for calling only from gdb. They cross abstraction boundaries and allow quickly accessing one thing from another thing.
I expect to grow this library significantly over time to aid debugging tricky problems.

Add missing files to BUILD

Mostly this is code copied from bm_fullstack and rephrased as a test.
I'm resisting the urge to unify it however, as I expect this code will evolve differently over time.

This reverts commit 5e01e2ac.

memory usage profiling for client call, client channel, server creation, server call and server channel.

fix bug. server: snapshot pass by pointer