Add a spinlock type.

PHP: added README notes for RHEL 6/7 users

Enable Go Negative HTTP2 Interop Test

Add zalloc, convert a bunch of files to use it

Add more cq benchmarks

Client-side keepalive pings

Make portability tests pull images from Dockerhub and add test filter

Stop receiving and add an error to batch when there is an error from lower level.

Upmerge 1.1.x into master

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.

Display logs when running interop based tests

Based on soltanmm-google's #9114

Fix uploader

Add benchmarks for metadata operations

Add benchmarks for HTTP2 HPACK encoding

Increase timeout for bm_fullstack

Add grpc_load_reporting to grpc_cronet

Fix closure running: current code is unsafe