Make UTF16ToASCII and UTF16TOUTF8 take a StringPiece

content/child/simple_webmimeregistry_impl.cc

Index: content/child/simple_webmimeregistry_impl.cc
diff --git a/content/child/simple_webmimeregistry_impl.cc b/content/child/simple_webmimeregistry_impl.cc
index a25e2aecdfb459ed56a3249cd1e267ecf9dd199e..a3b1c7f527beea55a10f839431abcca83299efa4 100644
--- a/content/child/simple_webmimeregistry_impl.cc
+++ b/content/child/simple_webmimeregistry_impl.cc
@@ -19,8 +19,9 @@ namespace content {
 
 //static
 std::string SimpleWebMimeRegistryImpl::ToASCIIOrEmpty(const WebString& string) {
-  return base::IsStringASCII(string) ? base::UTF16ToASCII(string)
-                                     : std::string();
+  return base::IsStringASCII(string)
+      ? base::UTF16ToASCII(base::StringPiece16(string))
+      : std::string();
 }
 
 WebMimeRegistry::SupportsType SimpleWebMimeRegistryImpl::supportsMIMEType(