Make UTF16ToASCII and UTF16TOUTF8 take a StringPiece

components/html_viewer/web_mime_registry_impl.cc

Index: components/html_viewer/web_mime_registry_impl.cc
diff --git a/components/html_viewer/web_mime_registry_impl.cc b/components/html_viewer/web_mime_registry_impl.cc
index caed08920b74a5456852d0d32b5905d5c014577f..d3321aa432437b84f844cd7f0646109f6649387c 100644
--- a/components/html_viewer/web_mime_registry_impl.cc
+++ b/components/html_viewer/web_mime_registry_impl.cc
@@ -19,8 +19,9 @@ namespace html_viewer {
 namespace {
 
 std::string ToASCIIOrEmpty(const blink::WebString& string) {
-  return base::IsStringASCII(string) ? base::UTF16ToASCII(string)
-                                     : std::string();
+  return base::IsStringASCII(string)
+      ? base::UTF16ToASCII(base::StringPiece16(string))
+      : std::string();
 }
 
 }  // namespace