Structured cloning: improve DataCloneError reporting.

Source/core/dom/MessagePort.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 59 matching lines @@
         return;
     ASSERT(executionContext());
     ASSERT(m_entangledChannel);
 
     OwnPtr<MessagePortChannelArray> channels;
     // Make sure we aren't connected to any of the passed-in ports.
     if (ports) {
         for (unsigned int i = 0; i < ports->size(); ++i) {
             MessagePort* dataPort = (*ports)[i].get();
             if (dataPort == this) {
-                exceptionState.throwDOMException(DataCloneError, "Item #" + String::number(i) + " in the array of ports contains the source port.");
+                exceptionState.throwDOMException(DataCloneError, "Port at index " + String::number(i) + " contains the source port.");
                 return;
             }
         }
         channels = MessagePort::disentanglePorts(ports, exceptionState);
         if (exceptionState.hadException())
             return;
     }
 
     blink::WebString messageString = message->toWireString();
     blink::WebMessagePortChannelArray* webChannels = 0;
@@ skipping 114 matching lines @@
     for (unsigned i = 0; i < ports->size(); ++i) {
         MessagePort* port = (*ports)[i].get();
         if (!port || port->isNeutered() || portSet.contains(port)) {
             String type;
             if (!port)
                 type = "null";
             else if (port->isNeutered())
                 type = "already neutered";
             else
                 type = "a duplicate";
-            exceptionState.throwDOMException(DataCloneError, "Item #"  + String::number(i) + " in the array of ports is " + type + ".");
+            exceptionState.throwDOMException(DataCloneError, "Port at index "  + String::number(i) + " is " + type + ".");
             return nullptr;
         }
         portSet.add(port);
     }
 
     // Passed-in ports passed validity checks, so we can disentangle them.
     OwnPtr<MessagePortChannelArray> portArray = adoptPtr(new MessagePortChannelArray(ports->size()));
     for (unsigned i = 0; i < ports->size(); ++i)
         (*portArray)[i] = (*ports)[i]->disentangle();
     return portArray.release();
 }
 
 PassOwnPtr<MessagePortArray> MessagePort::entanglePorts(ExecutionContext& context, PassOwnPtr<MessagePortChannelArray> channels)
 {
     if (!channels || !channels->size())
         return nullptr;
 
     OwnPtr<MessagePortArray> portArray = adoptPtr(new MessagePortArray(channels->size()));
     for (unsigned int i = 0; i < channels->size(); ++i) {
         RefPtr<MessagePort> port = MessagePort::create(context);
         port->entangle((*channels)[i].release());
         (*portArray)[i] = port.release();
     }
     return portArray.release();
 }
 
 } // namespace WebCore