Fix potential flakiness of SocketStreamCloseTest.

runtime/bin/socket_impl.dart

Index: runtime/bin/socket_impl.dart
diff --git a/runtime/bin/socket_impl.dart b/runtime/bin/socket_impl.dart
index 6b5293601a2e964728fcfe31f2d85f7fe6207a87..04d5965e9780109ad418603ff8c667def631db55 100644
--- a/runtime/bin/socket_impl.dart
+++ b/runtime/bin/socket_impl.dart
@@ -58,7 +58,7 @@ class _SocketBase {
 
           // Don't call the in handler if there is no data available
           // after all.
-          if (i == _IN_EVENT && this is _Socket && available() == 0) {
+          if ((i == _IN_EVENT) && (this is _Socket) && (available() == 0)) {
             continue;
           }
           eventHandler();
@@ -132,28 +132,34 @@ class _SocketBase {
   }
 
   void _closeWrite() {
-    if (_closedRead) {
-      _close();
-    } else {
-      _sendToEventHandler(1 << _SHUTDOWN_WRITE_COMMAND);
+    if (_id >= 0) {
+      if (_closedRead) {
+        _close();
+      } else {
+        _sendToEventHandler(1 << _SHUTDOWN_WRITE_COMMAND);
+      }
+      _closedWrite = true;
     }
-    _closedWrite = true;
   }
 
   void _closeRead() {
-    if (_closedWrite) {
-      _close();
-    } else {
-      _sendToEventHandler(1 << _SHUTDOWN_READ_COMMAND);
+    if (_id >= 0) {
+      if (_closedWrite) {
+        _close();
+      } else {
+        _sendToEventHandler(1 << _SHUTDOWN_READ_COMMAND);
+      }
+      _closedRead = true;
     }
-    _closedRead = true;
   }
 
   void _close() {
-    _sendToEventHandler(1 << _CLOSE_COMMAND);
-    _handler.close();
-    _handler = null;
-    _id = -1;
+    if (_id >= 0) {
+      _sendToEventHandler(1 << _CLOSE_COMMAND);
+      _handler.close();
+      _handler = null;
+      _id = -1;
+    }
   }
 
   void _sendToEventHandler(int data) {