Add support for implicitly concatenating adjacent string literals.

frog/analyze.dart

 // Copyright (c) 2012, 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.
 
 /**
  * A simple code analyzer for Dart.
  *
  * Currently used to ensure all concrete generic types are visited.
  * Also performs all static type checks - so these don't need to be
  * done in later phases.
@@ skipping 756 matching lines @@
   }
 
   Value visitSuperExpression(SuperExpression node) {
     return _frame.makeSuperValue(node);
   }
 
   Value visitLiteralExpression(LiteralExpression node) {
     return new PureStaticValue(node.value.type, node.span, true);
   }
 
+  Value visitStringConcatExpression(StringConcatExpression node) {
+    node.strings.forEach(visitValue);
+    return _frame._makeValue(world.stringType, node);
+  }
+
   Value visitStringInterpExpression(StringInterpExpression node) {
     node.pieces.forEach(visitValue);
     return _frame._makeValue(world.stringType, node);
 
     // TODO(jimhug): Do we need this more elaborate analysis?
     /*
     var ret = Value.fromString('', node.span);
 
     for (var item in node.pieces) {
       var val = visitValue(item);
       var sval = val.invoke(_frame, 'toString', item, Arguments.EMPTY);
       ret = ret.binop(TokenKind.ADD, sval, _frame, item);
     }
     return _frame._makeValue(world.stringType, node); //???ret;
     */
   }
 }