Handle potentially const interpolation

runtime/vm/ast.cc

Index: runtime/vm/ast.cc
diff --git a/runtime/vm/ast.cc b/runtime/vm/ast.cc
index 48bd0534e0b425094f3e700caaeeb38ae81486c7..8698e26baf59c6dbf19da96d7719500fb99b3265 100644
--- a/runtime/vm/ast.cc
+++ b/runtime/vm/ast.cc
@@ -122,6 +122,16 @@ void ArrayNode::VisitChildren(AstNodeVisitor* visitor) const {
 }
 
 
+bool StringInterpolateNode::IsPotentiallyConst() const {
+  for (int i = 0; i < value_->length(); i++) {
+    if (!value_->ElementAt(i)->IsPotentiallyConst()) {
+      return false;
+    }
+  }
+  return true;
+}
+
+
 bool LiteralNode::IsPotentiallyConst() const {
   return true;
 }