[EventEngine] Simple iOS EventEngine experiment configuration. (#32782)

cc @sampajano

src/core/lib/event_engine/shim.cc

@@ -29,6 +29,8 @@ bool UseEventEngineClient() {
   return grpc_core::IsEventEngineClientEnabled();
 #elif defined(GPR_WINDOWS)
   return grpc_core::IsEventEngineClientEnabled();
+#elif defined(GRPC_IOS_EVENT_ENGINE_CLIENT)
+  return true;
 #else
   return false;
 #endif

tools/internal_ci/macos/pull_request/grpc_bazel_cpp_ios_event_engine_experiment_tests.cfg

@@ -0,0 +1,42 @@
+# Copyright 2023 The gRPC Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Config file for the internal CI (in protobuf text format)
+
+# Location of the continuous shell script in repository.
+build_file: "grpc/tools/internal_ci/macos/grpc_run_bazel_cpp_ios_tests.sh"
+timeout_mins: 90
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.*"
+    regex: "github/grpc/reports/**"
+  }
+}
+
+gfile_resources: "/bigstore/grpc-testing-secrets/gcp_credentials/GrpcTesting-d0eeee2db331.json"
+gfile_resources: "/bigstore/grpc-testing-secrets/gcp_credentials/resultstore_api_key"
+
+bazel_setting {
+  # In order for Kokoro to recognize this as a bazel build and publish the bazel resultstore link,
+  # the bazel_setting section needs to be present and "upsalite_frontend_address" needs to be
+  # set. The rest of configuration from bazel_setting is unused (we configure everything when bazel
+  # command is invoked).
+  upsalite_frontend_address: "https://source.cloud.google.com"
+}
+
+env_vars {
+  # flags will be passed to bazel invocation
+  key: "BAZEL_FLAGS"
+  value: "--config=dbg --cxxopt=-DGRPC_IOS_EVENT_ENGINE_CLIENT=1"
+}