Add CompilationUnitElement.lineInfo and resynthesize it.

pkg/analyzer/lib/src/summary/resynthesize.dart

Index: pkg/analyzer/lib/src/summary/resynthesize.dart
diff --git a/pkg/analyzer/lib/src/summary/resynthesize.dart b/pkg/analyzer/lib/src/summary/resynthesize.dart
index 68c3017d5437bd1e923554e92c047b9a56d0cd5d..aeec4b4c2a5b3597d0f27363e925a5d8723297af 100644
--- a/pkg/analyzer/lib/src/summary/resynthesize.dart
+++ b/pkg/analyzer/lib/src/summary/resynthesize.dart
@@ -1508,6 +1508,15 @@ class _UnitResynthesizer {
         unlinkedUnit,
         unlinkedPart,
         unitSource.shortName);
+
+    {
+      List<int> lineStarts = unlinkedUnit.lineStarts;
+      if (lineStarts.isEmpty) {
+        lineStarts = const <int>[0];
+      }
+      unit.lineInfo = new LineInfo(lineStarts);
+    }
+
     for (EntityRef t in linkedUnit.types) {
       linkedTypeMap[t.slot] = t;
     }