Introduce no-op --experimental_google_legacy_api flag

This flag will be used to guard a substantial amount of experimental-only Starlark Build API pertaining to Google legacy code.

RELNOTES: None.
PiperOrigin-RevId: 244378067
diff --git a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
index 6b6e84b..08eeec2 100644
--- a/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
+++ b/src/test/java/com/google/devtools/build/lib/packages/SkylarkSemanticsConsistencyTest.java
@@ -124,6 +124,7 @@
             + ","
             + rand.nextDouble(),
         "--experimental_enable_android_migration_apis=" + rand.nextBoolean(),
+        "--experimental_google_legacy_api=" + rand.nextBoolean(),
         "--experimental_java_common_create_provider_enabled_packages="
             + rand.nextDouble()
             + ","
@@ -175,6 +176,7 @@
         .experimentalCcSkylarkApiEnabledPackages(
             ImmutableList.of(String.valueOf(rand.nextDouble()), String.valueOf(rand.nextDouble())))
         .experimentalEnableAndroidMigrationApis(rand.nextBoolean())
+        .experimentalGoogleLegacyApi(rand.nextBoolean())
         .experimentalJavaCommonCreateProviderEnabledPackages(
             ImmutableList.of(String.valueOf(rand.nextDouble()), String.valueOf(rand.nextDouble())))
         .experimentalPlatformsApi(rand.nextBoolean())