Handle const Symbol(...) in kernel_impact

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

Index: pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
diff --git a/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart b/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
index c52f3cc69a3c503173ec16c09d4f14d1cdc29997..b61e31461bfd19677a8638936df09838e350e8bd 100644
--- a/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
+++ b/pkg/compiler/lib/src/ssa/kernel_ast_adapter.dart
@@ -85,6 +85,11 @@ class KernelAstAdapter extends KernelElementAdapterMixin {
     _typeConverter = new DartTypeConverter(this);
   }
 
+  @override
+  ConstantValue computeConstantValue(ConstantExpression constant) {
+    return _compiler.constants.getConstantValue(constant);
+  }
+
   /// Called to find the corresponding Kernel element for a particular Element
   /// before traversing over it with a Kernel visitor.
   ir.Node getInitialKernelNode(Element originTarget) {