test_runner: Do not dump validation messages for web-platform-tests.

components/test_runner/web_view_test_client.cc

Index: components/test_runner/web_view_test_client.cc
diff --git a/components/test_runner/web_view_test_client.cc b/components/test_runner/web_view_test_client.cc
index 446acdaa509d9f4ebbdf0c76de7910b32c547cf5..ce689deccda6fb11b7429a9a1e166f67a96a28de 100644
--- a/components/test_runner/web_view_test_client.cc
+++ b/components/test_runner/web_view_test_client.cc
@@ -109,6 +109,9 @@ void WebViewTestClient::showValidationMessage(
     blink::WebTextDirection main_message_hint,
     const blink::WebString& sub_message,
     blink::WebTextDirection sub_message_hint) {
+  if (test_runner_->is_web_platform_tests_mode())
+    return;
+
   base::string16 wrapped_main_text = main_message;
   base::string16 wrapped_sub_text = sub_message;