dart2js: Use frequency of occurence to sort metadata indices.

pkg/compiler/lib/src/ssa/codegen_helpers.dart

Index: pkg/compiler/lib/src/ssa/codegen_helpers.dart
diff --git a/pkg/compiler/lib/src/ssa/codegen_helpers.dart b/pkg/compiler/lib/src/ssa/codegen_helpers.dart
index e6bf13d27619c7f4deb82416127d26deeda8c817..43ca710422f00cbcb8db012705787dd411a73d58 100644
--- a/pkg/compiler/lib/src/ssa/codegen_helpers.dart
+++ b/pkg/compiler/lib/src/ssa/codegen_helpers.dart
@@ -120,7 +120,8 @@ class SsaInstructionSelection extends HBaseVisitor {
           // TODO(15933): Make automatically generated property extraction
           // closures work with the dummy receiver optimization.
           if (!selector.isGetter) {
-            ConstantValue constant = new DummyConstantValue(
+            ConstantValue constant = new SyntheticConstantValue(
+                SyntheticConstantKind.DUMMY_INTERCEPTOR,
                 receiverArgument.instructionType);
             HConstant dummy = graph.addConstant(constant, compiler);
             receiverArgument.usedBy.remove(node);