Make string juxtaposition combine properly with string interpolations.

frog/leg/ssa/nodes.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 interface HVisitor<R> {
   R visitAdd(HAdd node);
   R visitBailoutTarget(HBailoutTarget node);
   R visitBitAnd(HBitAnd node);
   R visitBitNot(HBitNot node);
   R visitBitOr(HBitOr node);
@@ skipping 1362 matching lines @@
     if (input == target) return HType.UNKNOWN;
     if (isString() || left.isString()) {
       return (input == left) ? HType.STRING : HType.UNKNOWN;
     }
     if (right.isString()) return HType.STRING;
     if (isNumber() || left.isNumber() || right.isNumber()) return HType.NUMBER;
     return HType.UNKNOWN;
   }
 
   AddOperation get operation() => const AddOperation();
+
   int typeCode() => 5;
   bool typeEquals(other) => other is HAdd;
   bool dataEquals(HInstruction other) => true;
 }
 
 class HDivide extends HBinaryArithmetic {
   HDivide(HStatic target, HInstruction left, HInstruction right)
       : super(target, left, right);
   accept(HVisitor visitor) => visitor.visitDivide(this);
 
@@ skipping 738 matching lines @@
 class HIfBlockInformation {
   final HIf branch;
   final SubGraph thenGraph;
   final SubGraph elseGraph;
   final HBasicBlock joinBlock;
   HIfBlockInformation(this.branch,
                       this.thenGraph,
                       this.elseGraph,
                       this.joinBlock);
 }