support Flaky=True for grpc_cc_tests

bazel/grpc_build_system.bzl

@@ -168,7 +168,7 @@ def ios_cc_test(
             deps = ios_test_deps,
         )
 
-def grpc_cc_test(name, srcs = [], deps = [], external_deps = [], args = [], data = [], uses_polling = True, language = "C++", size = "medium", timeout = None, tags = [], exec_compatible_with = [], exec_properties = {}, shard_count = None):
+def grpc_cc_test(name, srcs = [], deps = [], external_deps = [], args = [], data = [], uses_polling = True, language = "C++", size = "medium", timeout = None, tags = [], exec_compatible_with = [], exec_properties = {}, shard_count = None, flaky = None):
     copts = if_mac(["-DGRPC_CFSTREAM"])
     if language.upper() == "C":
         copts = copts + if_not_windows(["-std=c99"])
@@ -187,6 +187,7 @@ def grpc_cc_test(name, srcs = [], deps = [], external_deps = [], args = [], data
         "exec_compatible_with": exec_compatible_with,
         "exec_properties": exec_properties,
         "shard_count": shard_count,
+        "flaky": flaky,
     }
     if uses_polling:
         # the vanilla version of the test should run on platforms that only
@@ -218,6 +219,7 @@ def grpc_cc_test(name, srcs = [], deps = [], external_deps = [], args = [], data
                 exec_compatible_with = exec_compatible_with,
                 exec_properties = exec_properties,
                 shard_count = shard_count,
+                flaky = flaky,
             )
     else:
         # the test behavior doesn't depend on polling, just generate the test