Implement Symbol correctly in dart2js.

dart/sdk/lib/_internal/compiler/implementation/ssa/builder.dart

Index: dart/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/ssa/builder.dart b/dart/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
index ea348f71dfc4f73529f7d843c12eb66ba32f06be..37829d7c3c4f4cab131939d52c1644da8e0abbb7 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/ssa/builder.dart
@@ -3342,6 +3342,18 @@ class SsaBuilder extends ResolvedVisitor implements Visitor {
     }
     FunctionElement functionElement = constructor;
     constructor = functionElement.redirectionTarget;
+    final bool isSymbolConstructor =
+        functionElement == compiler.symbolConstructor;
+
+    if (isSymbolConstructor) {
+      constructor = compiler.symbolValidatedConstructor;
+      assert(invariant(node, constructor != null,
+                       message: 'Constructor Symbol.validated is missing'));
+      selector = compiler.symbolValidatedConstructorSelector;
+      assert(invariant(node, selector != null,
+                       message: 'Constructor Symbol.validated is missing'));
+    }
+
     // TODO(5346): Try to avoid the need for calling [declaration] before
     // creating an [HStatic].
     HInstruction target = new HStatic(constructor.declaration);