Make UTF16ToASCII and UTF16TOUTF8 take a StringPiece

media/blink/webencryptedmediaclient_impl.cc

Index: media/blink/webencryptedmediaclient_impl.cc
diff --git a/media/blink/webencryptedmediaclient_impl.cc b/media/blink/webencryptedmediaclient_impl.cc
index fd45ad7cf32888e8ae1e3bf9b352da167ee00e75..940805b8e6db3d162cbc4b4e0e0d089d973e2acb 100644
--- a/media/blink/webencryptedmediaclient_impl.cc
+++ b/media/blink/webencryptedmediaclient_impl.cc
@@ -151,7 +151,7 @@ WebEncryptedMediaClientImpl::Reporter* WebEncryptedMediaClientImpl::GetReporter(
   // TODO(sandersd): Avoid doing ASCII conversion more than once.
   std::string key_system_ascii;
   if (base::IsStringASCII(key_system))
-    key_system_ascii = base::UTF16ToASCII(key_system);
+    key_system_ascii = base::UTF16ToASCII(base::StringPiece16(key_system));
 
   // Return a per-frame singleton so that UMA reports will be once-per-frame.
   std::string uma_name = GetKeySystemNameForUMA(key_system_ascii);