dart2js: Use frequency of occurence to sort metadata indices.

pkg/js_ast/lib/src/template.dart

Index: pkg/js_ast/lib/src/template.dart
diff --git a/pkg/js_ast/lib/src/template.dart b/pkg/js_ast/lib/src/template.dart
index e7aa86349138ef90b14c60f729f5dfb6da4d4d33..c3dca1979305d90083a67b65ca9b2a6f4ab40b6a 100644
--- a/pkg/js_ast/lib/src/template.dart
+++ b/pkg/js_ast/lib/src/template.dart
@@ -654,6 +654,13 @@ class InstantiatorGeneratorVisitor implements NodeVisitor<Instantiator> {
     };
   }
 
+  Instantiator visitDeferredExpression(DeferredExpression node) => same(node);
+
+  Instantiator visitDeferredNumber(DeferredNumber node) => same(node);
+
+  Instantiator visitDeferredString(DeferredString node) =>
+      (arguments) => node;
+
   Instantiator visitLiteralBool(LiteralBool node) =>
       (arguments) => new LiteralBool(node.value);
 
@@ -666,6 +673,18 @@ class InstantiatorGeneratorVisitor implements NodeVisitor<Instantiator> {
   Instantiator visitLiteralNull(LiteralNull node) =>
       (arguments) => new LiteralNull();
 
+  Instantiator visitStringConcatenation(StringConcatenation node) {
+    List<Instantiator> partMakers = node.parts
+        .map(visit)
+        .toList(growable: false);
+    return (arguments) {
+      List<Literal> parts = partMakers
+          .map((Instantiator instantiator) => instantiator(arguments))
+          .toList(growable: false);
+      return new StringConcatenation(parts);
+    };
+  }
+
   Instantiator visitArrayInitializer(ArrayInitializer node) {
     // TODO(sra): Implement splicing?
     List<Instantiator> elementMakers = node.elements