Move enable extensions define to a build flag.

tools/json_schema_compiler/test/BUILD.gn

Index: tools/json_schema_compiler/test/BUILD.gn
diff --git a/tools/json_schema_compiler/test/BUILD.gn b/tools/json_schema_compiler/test/BUILD.gn
index fe124f0e8c5435e4dde833a6cbd1098b241d6140..95a7a8705a9a5329399c100dec69a5f2b97cb4a0 100644
--- a/tools/json_schema_compiler/test/BUILD.gn
+++ b/tools/json_schema_compiler/test/BUILD.gn
@@ -4,8 +4,11 @@
 
 import("//build/config/features.gni")
 import("//build/json_schema_api.gni")
+import("//extensions/features/features.gni")
 import("//tools/json_schema_compiler/json_features.gni")
 
+assert(enable_extensions)
+
 json_schema_api("api") {
   visibility = [ ":*" ]
 
@@ -32,22 +35,37 @@ json_schema_api("api") {
 
   schemas = true
   root_namespace = "test::api::%(namespace)s"
+
+  deps = [
+    "//extensions/features",
+  ]
 }
 
-if (enable_extensions) {
-  json_features("features_compiler_test") {
-    feature_class = "APIFeature"
-    provider_class = "CompilerTestFeatureProvider"
-    sources = [
-      "features_test.json",
-      "features_test2.json",
-    ]
-  }
+json_features("features_compiler_test") {
+  feature_class = "APIFeature"
+  provider_class = "CompilerTestFeatureProvider"
+  sources = [
+    "features_test.json",
+    "features_test2.json",
+  ]
 }
 
-source_set("schema_test") {
+source_set("unit_tests") {
   testonly = true
   sources = [
+    "additional_properties_unittest.cc",
+    "any_unittest.cc",
+    "arrays_unittest.cc",
+    "callbacks_unittest.cc",
+    "choices_unittest.cc",
+    "crossref_unittest.cc",
+    "enums_unittest.cc",
+    "error_generation_unittest.cc",
+    "functions_as_parameters_unittest.cc",
+    "functions_on_types_unittest.cc",
+    "idl_schemas_unittest.cc",
+    "objects_unittest.cc",
+    "simple_api_unittest.cc",
     "test_util.cc",
     "test_util.h",
   ]
@@ -56,16 +74,12 @@ source_set("schema_test") {
   configs += [ "//build/config/compiler:no_size_t_to_int_warning" ]
 
   public_deps = [
+    ":features_compiler_test",
+  ]
+
+  deps = [
     ":api",
     "//base",
+    "//testing/gtest",
   ]
 }
-
-if (enable_extensions) {
-  source_set("features_generation_test") {
-    testonly = true
-    public_deps = [
-      ":features_compiler_test",
-    ]
-  }
-}