[blink-in-js] Migrate resources required for blink-in-js to grd - part 3

Source/core/BUILD.gn

Index: Source/core/BUILD.gn
diff --git a/Source/core/BUILD.gn b/Source/core/BUILD.gn
index 5eddca6809cee34f9ecc27cb288c88304442ae0e..a6f192a3a42429dd34b33b1b0aa9f22a85f5fbd4 100644
--- a/Source/core/BUILD.gn
+++ b/Source/core/BUILD.gn
@@ -942,7 +942,8 @@ action("make_core_generated_private_script_for_testing") {
     "$blink_core_output_dir/PrivateScriptSourcesForTesting.h",
   ]
 
-  args = rebase_path(outputs, root_build_dir)
+  args = [ "--for-testing" ]
+  args += rebase_path(outputs, root_build_dir)
   args += rebase_path(inputs, root_build_dir)
 
   deps = make_core_generated_deps