Add no-info mappings at start of out.js and after mapped functions

tests/compiler/dart2js/sourcemaps/load.dart

Index: tests/compiler/dart2js/sourcemaps/load.dart
diff --git a/tests/compiler/dart2js/sourcemaps/load.dart b/tests/compiler/dart2js/sourcemaps/load.dart
index 29cb8e096ad660f3b5812bf66c11d17c5c2e1c45..6553a0572691bb7144e3c286c2d1dc72db8de8d2 100644
--- a/tests/compiler/dart2js/sourcemaps/load.dart
+++ b/tests/compiler/dart2js/sourcemaps/load.dart
@@ -74,21 +74,21 @@ String convertToHumanReadableSourceMap(SingleMapping sourceMap) {
       } else {
         position = '$line,$columnStart-';
       }
+      if (needsComma) {
+        sb.write(',\n');
+      }
+      sb.write('    {"target": "$position"');
       if (entry.sourceUrlId != null) {
         int sourceUrlId = entry.sourceUrlId;
         int sourceLine = entry.sourceLine + 1;
         int sourceColumn = entry.sourceColumn + 1;
-        if (needsComma) {
-          sb.write(',\n');
-        }
-        sb.write('    {"target": "$position"');
         sb.write(', "source": "$sourceUrlId:$sourceLine,$sourceColumn"');
         if (entry.sourceNameId != null) {
           sb.write(', "name": "${sourceMap.names[entry.sourceNameId]}"');
         }
-        sb.write('}');
-        needsComma = true;
       }
+      sb.write('}');
+      needsComma = true;
     }
   }
   sb.write('\n  ]\n');