Update co19 test expectations to disable tests using String.concat.

tools/coverage.dart

 // Copyright (c) 2013, 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.
 
 // This test forks a second vm process that runs a dart script as
 // a debug target, single stepping through the entire program, and
 // recording each breakpoint. At the end, a coverage map of the source
 // is printed.
 //
 // Usage: dart coverage.dart [--wire] [--verbose] target_script.dart
@@ skipping 336 matching lines @@
     socket.write(jsonMsg);
   }
 
   void getLineNumberTable(String url, int libId) {
     queuedCommands.add(new GetLineTableCmd(isolateId, libId, url));
   }
 
   void getLibraries() {
     queuedCommands.add(new GetLibrariesCmd(isolateId));
   }
-  
+
   void enableDebugging(libraryId, enable) {
     queuedCommands.add(new SetLibraryPropertiesCmd(isolateId, libraryId, enable));
   }
 
   bool get errorsDetected => errors.length > 0;
 
   // Record error message.
   void error(String s) {
     errors.add(s);
   }
@@ skipping 66 matching lines @@
 
 // Class to buffer wire protocol data from coverage target and
 // break it down to individual json messages.
 class JsonBuffer {
   String buffer = null;
 
   append(String s) {
     if (buffer == null || buffer.length == 0) {
       buffer = s;
     } else {
-      buffer = buffer.concat(s);
+      buffer = buffer + s;
     }
   }
 
   String getNextMessage() {
     if (buffer == null) return null;
     int msgLen = objectLength();
     if (msgLen == 0) return null;
     String msg = null;
     if (msgLen == buffer.length) {
       msg = buffer;
       buffer = null;
     } else {
       assert(msgLen < buffer.length);
       msg = buffer.substring(0, msgLen);
       buffer = buffer.substring(msgLen);
     }
     return msg;
   }
 
   bool haveGarbage() {
     if (buffer == null || buffer.length == 0) return false;
     var i = 0, char = " ";
     while (i < buffer.length) {
       char = buffer[i];
       if (char != " " && char != "\n" && char != "\r" && char != "\t") break;
       i++;
     }
     if (i >= buffer.length) {
       return false;
-    } else { 
+    } else {
       return char != "{";
     }
   }
 
   // Returns the character length of the next json message in the
   // buffer, or 0 if there is only a partial message in the buffer.
   // The object value must start with '{' and continues to the
   // matching '}'. No attempt is made to otherwise validate the contents
   // as JSON. If it is invalid, a later JSON.decode() will fail.
   int objectLength() {
@@ skipping 53 matching lines @@
         targetOpts.add(str);
         break;
     }
   }
 
   Process.start(options.executable, targetOpts).then((Process process) {
     process.stdin.close();
     debugger = new Debugger(process);
   });
 }