Add a test that headers are properly in build.json

BUILD

Makefile

build.json

src/compiler/python_generator.cc

src/core/census/context.c

src/cpp/client/channel.cc

src/cpp/client/channel_arguments.cc

src/cpp/client/secure_channel_arguments.cc

src/cpp/server/insecure_server_credentials.cc

src/cpp/server/server.cc

src/cpp/server/server_credentials.cc

templates/tools/run_tests/sources_and_headers.json.template

test/core/bad_client/gen_build_json.py

test/core/end2end/gen_build_json.py

test/cpp/qps/qps_worker.cc

test/cpp/qps/worker.cc

tools/doxygen/Doxyfile.c++.internal

tools/run_tests/check_sources_and_headers.py

tools/run_tests/run_tests.py

tools/run_tests/sources_and_headers.json