dart2js: Use frequency of occurence to sort metadata indices.

pkg/compiler/lib/src/constants/expressions.dart

Index: pkg/compiler/lib/src/constants/expressions.dart
diff --git a/pkg/compiler/lib/src/constants/expressions.dart b/pkg/compiler/lib/src/constants/expressions.dart
index 0c6a6ac8795f0ace9761a22530c484b75f32e21f..13c799f8bb0a00b44e07e3d9e747f578a46cd8a2 100644
--- a/pkg/compiler/lib/src/constants/expressions.dart
+++ b/pkg/compiler/lib/src/constants/expressions.dart
@@ -28,6 +28,7 @@ enum ConstantExpressionKind {
   CONSTRUCTED,
   DEFERRED,
   DOUBLE,
+  DUMMY,
   ERRONEOUS,
   FUNCTION,
   IDENTICAL,
@@ -335,6 +336,34 @@ class ErroneousConstantExpression extends ConstantExpression {
   bool _equals(ErroneousConstantExpression other) => true;
 }
 
+class DummyConstantExpression extends ConstantExpression {

[Johnni Winther, 2015/05/28 12:07:17]

Add a TODO for me to see if we can avoid the need for this.

[herhut, 2015/06/01 12:09:41]

Done.

+  final DummyConstantValue value;
+
+  DummyConstantExpression(this.value);
+
+  @override
+  ConstantValue evaluate(Environment environment,
+                         ConstantSystem constantSystem) {
+    return value;
+  }
+
+  @override
+  int _computeHashCode() => 13 * value.hashCode;
+
+  accept(ConstantExpressionVisitor visitor, [context]) {
+    throw "unsupported";
+  }
+
+  @override
+  bool _equals(BoolConstantExpression other) {
+    return value == other.value;
+  }
+
+  ConstantExpressionKind get kind => ConstantExpressionKind.DUMMY;
+}
+
+
+
 /// A boolean, int, double, string, or null constant.
 abstract class PrimitiveConstantExpression extends ConstantExpression {
   final PrimitiveConstantValue value;