Use ASCII case conversion in color input validation.

All valid color strings are ASCII.

Bug: 627682
Change-Id: Ib169ff7c1014557ac50286435b443dc1e3104533
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1574210Reviewed-by: Hayato Ito <hayato@chromium.org>
Commit-Queue: Jeremy Roman <jbroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652669}

third_party/blink/renderer/core/html/forms/color_input_type.cc

@@ -112,7 +112,7 @@ bool ColorInputType::SupportsRequired() const {
 String ColorInputType::SanitizeValue(const String& proposed_value) const {
   if (!IsValidColorString(proposed_value))
     return "#000000";
-  return proposed_value.DeprecatedLower();
+  return proposed_value.LowerASCII();
 }
 
 Color ColorInputType::ValueAsColor() const {