[dart:io] Adds a finalizer to _NativeSocket to avoid socket leaks

runtime/bin/process.h

Index: runtime/bin/process.h
diff --git a/runtime/bin/process.h b/runtime/bin/process.h
index fafff6b8f59af589e859c0013d0f05ad1504c783..734db37c84103801a3a00fd67935c59896f35c90 100644
--- a/runtime/bin/process.h
+++ b/runtime/bin/process.h
@@ -73,7 +73,8 @@ enum ProcessSignals {
   kSigprof = 27,
   kSigwinch = 28,
   kSigpoll = 29,
-  kSigsys = 31
+  kSigsys = 31,
+  kLastSignal = kSigsys,
 };
 
 
@@ -139,6 +140,7 @@ class Process {
 
   static intptr_t SetSignalHandler(intptr_t signal);
   static void ClearSignalHandler(intptr_t signal);
+  static void ClearAllSignalHandlers();
 
   static Dart_Handle GetProcessIdNativeField(Dart_Handle process,
                                              intptr_t* pid);