Make UTF16ToASCII and UTF16TOUTF8 take a StringPiece

content/renderer/media/rtc_dtmf_sender_handler.cc

Index: content/renderer/media/rtc_dtmf_sender_handler.cc
diff --git a/content/renderer/media/rtc_dtmf_sender_handler.cc b/content/renderer/media/rtc_dtmf_sender_handler.cc
index f33591135875682ffb1ccf42323f74a8ded7e9ac..65ddd28961ac307a5b36fe880b78155e8f2ab009 100644
--- a/content/renderer/media/rtc_dtmf_sender_handler.cc
+++ b/content/renderer/media/rtc_dtmf_sender_handler.cc
@@ -79,7 +79,7 @@ bool RtcDtmfSenderHandler::canInsertDTMF() {
 bool RtcDtmfSenderHandler::insertDTMF(const blink::WebString& tones,
                                       long duration,
                                       long interToneGap) {
-  std::string utf8_tones = base::UTF16ToUTF8(tones);
+  std::string utf8_tones = base::UTF16ToUTF8(base::StringPiece16(tones));
   return dtmf_sender_->InsertDtmf(utf8_tones, static_cast<int>(duration),
                                   static_cast<int>(interToneGap));
 }