[EventEngine] Enable Windows EventEngine client in production builds (#36572)

This has been stable in CI since May 1st (over a week), zero flakes in EE client-enabled end2end tests.

Closes #36572

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36572 from drfloob:enable-win-ee-client 8f733316ee
PiperOrigin-RevId: 632233766

bazel/experiments.bzl

@@ -60,16 +60,12 @@ EXPERIMENTS = {
         },
         "off": {
             "core_end2end_test": [
-                "event_engine_client",
                 "promise_based_server_call",
             ],
             "endpoint_test": [
                 "tcp_frame_size_tuning",
                 "tcp_rcv_lowat",
             ],
-            "event_engine_client_test": [
-                "event_engine_client",
-            ],
             "flow_control_test": [
                 "multiping",
                 "peer_state_based_framing",
@@ -87,11 +83,15 @@ EXPERIMENTS = {
         },
         "on": {
             "core_end2end_test": [
+                "event_engine_client",
                 "event_engine_listener",
             ],
             "cpp_lb_end2end_test": [
                 "pick_first_new",
             ],
+            "event_engine_client_test": [
+                "event_engine_client",
+            ],
             "event_engine_listener_test": [
                 "event_engine_listener",
             ],

src/core/lib/experiments/experiments.cc

@@ -358,7 +358,7 @@ const ExperimentMetadata g_experiment_metadata[] = {
     {"client_privacy", description_client_privacy,
      additional_constraints_client_privacy, nullptr, 0, false, false},
     {"event_engine_client", description_event_engine_client,
-     additional_constraints_event_engine_client, nullptr, 0, false, true},
+     additional_constraints_event_engine_client, nullptr, 0, true, true},
     {"event_engine_dns", description_event_engine_dns,
      additional_constraints_event_engine_dns, nullptr, 0, false, false},
     {"event_engine_listener", description_event_engine_listener,

src/core/lib/experiments/experiments.h

@@ -100,7 +100,8 @@ inline bool IsCallStatusOverrideOnCancellationEnabled() { return true; }
 inline bool IsCallV3Enabled() { return false; }
 inline bool IsCanaryClientPrivacyEnabled() { return false; }
 inline bool IsClientPrivacyEnabled() { return false; }
-inline bool IsEventEngineClientEnabled() { return false; }
+#define GRPC_EXPERIMENT_IS_INCLUDED_EVENT_ENGINE_CLIENT
+inline bool IsEventEngineClientEnabled() { return true; }
 inline bool IsEventEngineDnsEnabled() { return false; }
 #define GRPC_EXPERIMENT_IS_INCLUDED_EVENT_ENGINE_LISTENER
 inline bool IsEventEngineListenerEnabled() { return true; }

src/core/lib/experiments/rollouts.yaml

@@ -58,9 +58,7 @@
     # not tested on iOS at all
     ios: broken
     posix: false
-    # TODO(hork): resolve when the client end2end test flake rate reduces to
+    windows: true
-    # a tolerable amount.
-    windows: false
 - name: event_engine_dns
   default:
     # not tested on iOS at all