Implement mac support for having multiple Dart_Port's registered on one OS socket

runtime/bin/eventhandler.h

 // Copyright (c) 2012, 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.
 
 #ifndef BIN_EVENTHANDLER_H_
 #define BIN_EVENTHANDLER_H_
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 #include "bin/isolate_data.h"
@@ skipping 309 matching lines @@
     if (port_ != 0) {
       DartUtils::PostInt32(port_, events);
     }
     if (!disable_tokens_) {
       tokens_--;
     }
   }
 
   virtual void ReturnTokens(Dart_Port port, int count) {
     ASSERT(port_ == port);
-    ASSERT(tokens_ >= 0);
     if (!disable_tokens_) {
       tokens_ += count;
     }
     ASSERT(tokens_ <= kTokenCount);
   }
 
   virtual intptr_t Mask() {
     if (tokens_ <= 0) {
       return 0;
     }
@@ skipping 200 matching lines @@
     }
   }
 
   virtual void ReturnTokens(Dart_Port port, int count) {
     HashMap::Entry* entry = tokens_map_.Lookup(
         GetHashmapKeyFromPort(port), GetHashmapHashFromPort(port), false);
     ASSERT(entry != NULL);
 
     PortEntry* pentry = reinterpret_cast<PortEntry*>(entry->value);
     bool was_ready = pentry->IsReady();
-    ASSERT(pentry->token_count >= 0);
     if (!disable_tokens_) {
       pentry->token_count += count;
     }
     ASSERT(pentry->token_count <= kTokenCount);
     bool is_ready = pentry->token_count > 0 && pentry->IsReady();
     if (!was_ready && is_ready) {
       active_readers_.Add(pentry);
     }
   }
 
@@ skipping 67 matching lines @@
 
  private:
   friend class EventHandlerImplementation;
   EventHandlerImplementation delegate_;
 };
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // BIN_EVENTHANDLER_H_