Fixes leak of native File objects.

runtime/bin/file_linux.cc

Index: runtime/bin/file_linux.cc
diff --git a/runtime/bin/file_linux.cc b/runtime/bin/file_linux.cc
index 0cd9dec4469633f1a0d8ffda3524e3b633258b27..2bf2c2edaa9847089d3deb45758c0522e41fe3a1 100644
--- a/runtime/bin/file_linux.cc
+++ b/runtime/bin/file_linux.cc
@@ -38,7 +38,9 @@ class FileHandle {
 
 
 File::~File() {
-  Close();
+  if (!IsClosed()) {
+    Close();
+  }
   delete handle_;
 }
 
@@ -196,10 +198,7 @@ File* File::Open(const char* path, FileOpenMode mode) {
 
 
 File* File::OpenStdio(int fd) {
-  if ((fd < 0) || (2 < fd)) {
-    return NULL;
-  }
-  return new File(new FileHandle(fd));
+  return ((fd < 0) || (2 < fd)) ? NULL : new File(new FileHandle(fd));
 }