DevTools: support TRACE_VALUE_TYPE_COPY_STRING

Source/core/inspector/TraceEventDispatcher.cpp

 /*
 * Copyright (C) 2013 Google 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:
 *
 *     * Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
@@ skipping 133 matching lines @@
         if (!strcmp(name, m_argumentNames[i]))
             return i;
     }
     return kNotFound;
 }
 
 const TraceEvent::TraceValueUnion& TraceEventDispatcher::TraceEvent::parameter(const char* name, unsigned char expectedType) const
 {
     static WebCore::TraceEvent::TraceValueUnion missingValue;
     size_t index = findParameter(name);
+    ASSERT(isMainThread());
     if (index == kNotFound || m_argumentTypes[index] != expectedType) {
         ASSERT_NOT_REACHED();
         return missingValue;
     }
-    return *reinterpret_cast<const WebCore::TraceEvent::TraceValueUnion*>(m_argumentValues + index);
+    return m_argumentValues[index];
 }
 
 } // namespace WebCore