Mojo JS bindings: change module loading solution.

mojo/public/interfaces/bindings/tests/BUILD.gn

Index: mojo/public/interfaces/bindings/tests/BUILD.gn
diff --git a/mojo/public/interfaces/bindings/tests/BUILD.gn b/mojo/public/interfaces/bindings/tests/BUILD.gn
index 06d0f9548014c11d8e2da029e06a3ed3f17735ec..7ea79a67c22c65bf73d3b33af5d0ff1fd8a3581d 100644
--- a/mojo/public/interfaces/bindings/tests/BUILD.gn
+++ b/mojo/public/interfaces/bindings/tests/BUILD.gn
@@ -26,6 +26,7 @@ mojom("test_interfaces") {
     "validation_test_interfaces.mojom",
   ]
   public_deps = [
+    ":echo",
     ":test_mojom_import",
     ":test_mojom_import2",
   ]
@@ -198,3 +199,12 @@ mojom("test_no_sources") {
     ":test_interfaces",
   ]
 }
+
+mojom("echo") {
+  testonly = true
+  sources = [
+    "echo.mojom",
+    "echo_import.mojom",
+  ]
+  use_new_js_bindings = true
+}