if appending at end of file ensure newline

pkg/polymer/bin/new_entry.dart

 ///
 /// Script to create boilerplate for a Polymer element.
 /// Produces new .html entry point for a polymer app and updates the
 /// pubspec.yaml to reflect it.
 ///
 /// Run this script with pub run:
 ///
 ///     pub run polymer:new_entry <html_file>
 ///
 import 'dart:io';
@@ skipping 141 matching lines @@
       insertionPoint = transformersSourceSpan.start.offset;
       textToInsert = '- ';
     } else {
       insertionPoint = sourceSpan.start.offset;
       pubspecText = '${pubspecText.substring(0, insertionPoint)}'
           '${pubspecText.substring(sourceSpan.end.offset)}';
     }
   } else {
     // There were no transformers at all.
     insertionPoint = pubspecText.length;
-    textToInsert = 'transformers:\n- ';
+    var optionalNewline = pubspecText.endsWith('\n') ? '' : '\n';
+    textToInsert = '${optionalNewline}transformers:\n- ';
     entryPoints = [entryPoint];
   }
 
   // TODO(dgrove): Once dartbug.com/20409 is addressed, use that here.
   var entryPointsText = entryPoints.map((e) => '    - $e').join('\n');
 
   textToInsert =
 '''${textToInsert}polymer:
     entry_points:
 $entryPointsText''';
 
 
   if (insertionPoint == pubspecText.length) {
     pubspecText = '${pubspecText}${textToInsert}';
   } else {
     pubspecText = '${pubspecText.substring(0, insertionPoint)}'
         '${textToInsert}\n${pubspecText.substring(insertionPoint)}';
   }
 
   _writePubspec(pubspecPath, pubspecText);
   return true;
 }
 
 _writePubspec(String pubspecPath, String text) {
   new File(pubspecPath).writeAsStringSync(text);
 }