Mojo C++ bindings: fail validation test if no test data found and add data dependency.

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

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("../../../mojo_application.gni")
 
 source_set("tests") {
   testonly = true
 
   sources = [
@@ skipping 39 matching lines @@
     "//mojo/public/cpp/bindings:callback",
     "//mojo/public/cpp/system",
     "//mojo/public/cpp/test_support:test_utils",
     "//mojo/public/interfaces/bindings/tests:test_associated_interfaces",
     "//mojo/public/interfaces/bindings/tests:test_interfaces",
     "//mojo/public/interfaces/bindings/tests:test_interfaces_experimental",
     "//mojo/public/interfaces/bindings/tests:test_struct_traits_interfaces",
     "//testing/gtest",
   ]
 
+  data = [
+    "//mojo/public/interfaces/bindings/tests/data/validation/",
+  ]
+
   if (is_ios) {
     assert_no_deps = [ "//third_party/WebKit/*" ]
   } else {
     sources += [
       "pickle_unittest.cc",
       "struct_traits_unittest.cc",
     ]
 
     deps += [ "//mojo/public/interfaces/bindings/tests:test_interfaces_blink" ]
   }
@@ skipping 56 matching lines @@
 source_set("mojo_public_bindings_test_utils") {
   sources = [
     "validation_test_input_parser.cc",
     "validation_test_input_parser.h",
   ]
 
   deps = [
     "//mojo/public/c/system",
   ]
 }