Include source in kernel.

pkg/kernel/lib/binary/ast_to_binary.dart

Index: pkg/kernel/lib/binary/ast_to_binary.dart
diff --git a/pkg/kernel/lib/binary/ast_to_binary.dart b/pkg/kernel/lib/binary/ast_to_binary.dart
index 68f3687fca8d7ae7c7e5c3476f673a1c9146e046..5c50f032fbaf1b77f53481cc448e0854cdc0db1e 100644
--- a/pkg/kernel/lib/binary/ast_to_binary.dart
+++ b/pkg/kernel/lib/binary/ast_to_binary.dart
@@ -137,20 +137,25 @@ class BinaryPrinter extends Visitor {
     _importTable = new ProgramImportTable(program);
     _stringIndexer.build(program);
     writeStringTable(_stringIndexer);
-    writeUriToLineStarts(program);
+    writeUriToLineStartsAndSource(program);
     writeList(program.libraries, writeNode);
     writeMemberReference(program.mainMethod, allowNull: true);
     _flush();
   }
 
-  void writeUriToLineStarts(Program program) {
-    program.uriToLineStarts.keys.forEach((uri) {
+  void writeUriToLineStartsAndSource(Program program) {
+    program.uriToLineStartsAndSource.keys.forEach((uri) {
       _sourceUriIndexer.put(uri);
     });
     writeStringTable(_sourceUriIndexer);
     for (int i = 0; i < _sourceUriIndexer.entries.length; i++) {
       String uri = _sourceUriIndexer.entries[i].value;
-      List<int> lineStarts = program.uriToLineStarts[uri] ?? [];
+      LineStartsAndSource lineStartsAndSource =
+          program.uriToLineStartsAndSource[uri] ??

[Kevin Millikin (Google), 2016/12/20 12:03:33]

Can this be null?  It's not clear that it can, or how.

[jensj, 2016/12/20 13:30:22]

It iterates over all entries in StringIndexer, that always has a empty-string
entry. We don't have source information for that.

+              new LineStartsAndSource([], "");
+      String sourceCode = lineStartsAndSource.source;
+      writeStringTableEntry(sourceCode);
+      List<int> lineStarts = lineStartsAndSource.lineStarts;
       writeUInt30(lineStarts.length);
       int previousLineStart = 0;
       lineStarts.forEach((lineStart) {