Merge pull request #11000 from lyuxuan/poll_stat

src/core/lib/surface/completion_queue.c

src/core/lib/surface/completion_queue.h

src/proto/grpc/testing/control.proto

src/proto/grpc/testing/stats.proto

test/cpp/microbenchmarks/fullstack_fixtures.h

test/cpp/qps/client.h

test/cpp/qps/client_async.cc

test/cpp/qps/driver.cc

test/cpp/qps/qps_json_driver.cc

test/cpp/qps/report.cc

test/cpp/qps/report.h

test/cpp/qps/server.h

test/cpp/qps/server_async.cc