Make source information on conditions mandatory in CPS

pkg/compiler/lib/src/tree_ir/optimization/statement_rewriter.dart

 // Copyright (c) 2014, 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.
 
 library tree_ir.optimization.statement_rewriter;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
 import '../../io/source_information.dart';
 import '../../elements/elements.dart';
@@ skipping 740 matching lines @@
   }
 
   /// Converts a compoundable operator application into the right-hand side for
   /// use in a compound assignment, discarding the left-hand value.
   ///
   /// For example, for `x + y + z` it returns `y + z`.
   Expression contractCompoundableBuiltin(ApplyBuiltinOperator e) {
     assert(isCompoundableBuiltin(e));
     if (e.arguments.length > 2) {
       assert(e.operator == BuiltinOperator.StringConcatenate);
-      return new ApplyBuiltinOperator(e.operator, e.arguments.skip(1).toList());
+      return new ApplyBuiltinOperator(
+          e.operator,
+          e.arguments.skip(1).toList(),
+          e.sourceInformation);
     } else {
       return e.arguments[1];
     }
   }
 
   void destroyVariableUse(VariableUse node) {
     --node.variable.readCount;
   }
 
   Expression visitSetField(SetField node) {
@@ skipping 609 matching lines @@
 }
 
 /// Decrement the reference count for [e] if it is a variable use.
 void destroyPrimaryExpression(Expression e) {
   if (e is VariableUse) {
     --e.variable.readCount;
   } else {
     assert(e is This);
   }
 }