[kernel] Add offset to SwitchContinueStatement; add debugging test

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

 // Copyright (c) 2016, 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 fasta.body_builder;
 
 import 'package:kernel/ast.dart'
     hide InvalidExpression, InvalidInitializer, InvalidStatement;
 
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
@@ skipping 2976 matching lines @@
           push(deprecated_buildCompileTimeErrorStatement(
               "Can't find label '$name'.", continueKeyword.next.charOffset));
           return;
         }
         switchScope.forwardDeclareLabel(identifier.name,
             target = createGotoTarget(offsetForToken(identifier.token)));
       }
       if (target.isGotoTarget &&
           target.functionNestingLevel == functionNestingLevel) {
         ContinueSwitchStatement statement =
-            new KernelContinueSwitchStatement(null);
+            new KernelContinueSwitchStatement(null)
+              ..fileOffset = continueKeyword.charOffset;
         target.addGoto(statement);
         push(statement);
         return;
       }
     }
     if (target == null) {
       push(compileTimeErrorInLoopOrSwitch =
           deprecated_buildCompileTimeErrorStatement(
               "No target of continue.", continueKeyword.charOffset));
     } else if (!target.isContinueTarget) {
@@ skipping 814 matching lines @@
       return AsyncMarker.Async;
     } else {
       assert(identical(starToken.stringValue, "*"));
       return AsyncMarker.AsyncStar;
     }
   } else {
     return unhandled(asyncToken.lexeme, "asyncMarkerFromTokens",
         asyncToken.charOffset, null);
   }
 }