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

mojo/public/cpp/bindings/tests/validation_unittest.cc

Index: mojo/public/cpp/bindings/tests/validation_unittest.cc
diff --git a/mojo/public/cpp/bindings/tests/validation_unittest.cc b/mojo/public/cpp/bindings/tests/validation_unittest.cc
index ceeb4c121ebe1b679c980d927f365abc994767f6..d8993bf67a525363583129e9237774101bf5e051 100644
--- a/mojo/public/cpp/bindings/tests/validation_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/validation_unittest.cc
@@ -165,6 +165,7 @@ void RunValidationTests(const std::string& prefix,
   std::vector<std::string> names =
       EnumerateSourceRootRelativeDirectory(GetPath("", ""));
   std::vector<std::string> tests = GetMatchingTests(names, prefix);
+  ASSERT_FALSE(tests.empty());
 
   for (size_t i = 0; i < tests.size(); ++i) {
     Message message;