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..d2ef0092b4e27bc656e8415ff849abc36d477785 100644
--- a/tests/compiler/dart2js/sourcemaps/load.dart
+++ b/tests/compiler/dart2js/sourcemaps/load.dart
@@ -74,17 +74,19 @@ String convertToHumanReadableSourceMap(SingleMapping sourceMap) {
       } else {
         position = '$line,$columnStart-';
       }
-      if (entry.sourceUrlId != null) {
-        int sourceUrlId = entry.sourceUrlId;
-        int sourceLine = entry.sourceLine + 1;
-        int sourceColumn = entry.sourceColumn + 1;
+      if (entry.sourceUrlId != null || columnEnd == null) {
         if (needsComma) {
           sb.write(',\n');
         }
         sb.write('    {"target": "$position"');
-        sb.write(', "source": "$sourceUrlId:$sourceLine,$sourceColumn"');
-        if (entry.sourceNameId != null) {
-          sb.write(', "name": "${sourceMap.names[entry.sourceNameId]}"');
+        if (entry.sourceUrlId != null) {
+          int sourceUrlId = entry.sourceUrlId;
+          int sourceLine = entry.sourceLine + 1;
+          int sourceColumn = entry.sourceColumn + 1;
+          sb.write(', "source": "$sourceUrlId:$sourceLine,$sourceColumn"');
+          if (entry.sourceNameId != null) {
+            sb.write(', "name": "${sourceMap.names[entry.sourceNameId]}"');
+          }
         }
         sb.write('}');
         needsComma = true;