Move RTCPeerConnection to correct location to generate the supported check for

tools/dom/templates/html/impl/impl_RTCPeerConnection.darttemplate

Index: tools/dom/templates/html/impl/impl_RTCPeerConnection.darttemplate
===================================================================
--- tools/dom/templates/html/impl/impl_RTCPeerConnection.darttemplate	(working copy)
+++ tools/dom/templates/html/impl/impl_RTCPeerConnection.darttemplate	(working copy)
@@ -5,6 +5,7 @@
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
+$if DART2JS
   factory $CLASSNAME(Map rtcIceServers, [Map mediaConstraints]) {
     var constructorName = JS('RtcPeerConnection', 'window[#]',
         '${_browserPropertyPrefix}RTCPeerConnection');
@@ -17,6 +18,7 @@
           convertDartToNative_SerializedScriptValue(rtcIceServers));
     }
   }
+$endif
 
   /**
    * Checks if Real Time Communication (RTC) APIs are supported and enabled on