Corrects cleanup on an error during Process startup

runtime/bin/process_patch.dart

Index: runtime/bin/process_patch.dart
diff --git a/runtime/bin/process_patch.dart b/runtime/bin/process_patch.dart
index b6d40ee7a3eea18e8b8ee33fb6c0fd75f008734d..c6f9533eb68078130f2fc1d83febcdcb5f078c87 100644
--- a/runtime/bin/process_patch.dart
+++ b/runtime/bin/process_patch.dart
@@ -409,6 +409,7 @@ class _ProcessImpl extends _ProcessImplNativeWrapper with _ServiceObject
                            ? null : _exitHandler._nativeSocket,
                        status);
       if (!success) {
+        _processes.remove(_serviceId);
         completer.completeError(
             new ProcessException(_path,
                                  _arguments,
@@ -471,6 +472,7 @@ class _ProcessImpl extends _ProcessImplNativeWrapper with _ServiceObject
                                 _exitHandler._nativeSocket,
                                 status);
     if (!success) {
+      _processes.remove(_serviceId);
       throw new ProcessException(_path,
                                  _arguments,
                                  status._errorMessage,