Show form validation message as a fallback tooltip.

content/test/test_blink_web_unit_test_support.cc

Index: content/test/test_blink_web_unit_test_support.cc
diff --git a/content/test/test_blink_web_unit_test_support.cc b/content/test/test_blink_web_unit_test_support.cc
index 6f060587a8aab9d99b547e1fde27a97d6e1d1bcb..836e1aa5ccec0fea62eabda2769a3e5475d65862 100644
--- a/content/test/test_blink_web_unit_test_support.cc
+++ b/content/test/test_blink_web_unit_test_support.cc
@@ -222,6 +222,8 @@ blink::WebString TestBlinkWebUnitTestSupport::queryLocalizedString(
       return base::ASCIIToUTF16("<<ThisMonthLabel>>");
     case blink::WebLocalizedString::ThisWeekButtonLabel:
       return base::ASCIIToUTF16("<<ThisWeekLabel>>");
+    case blink::WebLocalizedString::ValidationValueMissing:
+      return base::ASCIIToUTF16("<<ValidationValueMissing>>");
     case blink::WebLocalizedString::WeekFormatTemplate:
       return base::ASCIIToUTF16("Week $2, $1");
     default: