Add chrome test support target to GN build.

components/search_engines/BUILD.gn

Index: components/search_engines/BUILD.gn
diff --git a/components/search_engines/BUILD.gn b/components/search_engines/BUILD.gn
index 260e457b140a53162282a6337d55bd73b57bb643..afc5be687d0f9bb2013d569d99154b933d2c4273 100644
--- a/components/search_engines/BUILD.gn
+++ b/components/search_engines/BUILD.gn
@@ -72,6 +72,21 @@ static_library("search_engines") {
   }
 }
 
+source_set("test_support") {
+  testonly = true
+  sources = [
+    "default_search_pref_test_util.cc",
+    "default_search_pref_test_util.h",
+    "testing_search_terms_data.cc",
+    "testing_search_terms_data.h",
+  ]
+
+  deps = [
+    ":search_engines",
+    "//testing/gtest",
+  ]
+}
+
 json_to_struct("prepopulated_engines") {
   visibility = [ ":*" ]