Use call context to propagare LR costs

Better error reporting in run_tests.py

Fix escaping in index.html

Add benchmarks of closures, combiners, exec_ctx primitives

Sanity improvements.

Lint fixes.

Possible connection window flow control improvements

Add a test that measures flow control stalls in a deterministic way

Signal that authority can be compressed in hpack: saves 1 allocation/rpc

Eliminate CQ freelist

This should have been included in 1a967c31.

The fix is more of an elision and the code in the changed area is
reflowed.

Added a script and config for bringing interop test to kokoro

Serialize running of perf, switch back to -f for consistent event counts

Run perf benchmarks in parallel

Store cython-level call in grpc.Call

Should only do host-->:authority if there is no :authority

Make latency traces more useful

Add flamegraphs to index.html