Show actualy FD for files in Observatory.

runtime/bin/file_linux.cc

 // 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.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_LINUX)
 
 #include "bin/file.h"
 
 #include <errno.h>  // NOLINT
@@ skipping 45 matching lines @@
     if (err != 0) {
       const int kBufferSize = 1024;
       char error_buf[kBufferSize];
       Log::PrintErr("%s\n", strerror_r(errno, error_buf, kBufferSize));
     }
   }
   handle_->set_fd(kClosedFd);
 }
 
 
+intptr_t File::GetFD() {
+  return handle_->fd();
+}
+
+
 bool File::IsClosed() {
   return handle_->fd() == kClosedFd;
 }
 
 
 int64_t File::Read(void* buffer, int64_t num_bytes) {
   ASSERT(handle_->fd() >= 0);
   return TEMP_FAILURE_RETRY(read(handle_->fd(), buffer, num_bytes));
 }
 
@@ skipping 345 matching lines @@
   return (file_1_info.st_ino == file_2_info.st_ino &&
           file_1_info.st_dev == file_2_info.st_dev) ?
       File::kIdentical :
       File::kDifferent;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_LINUX)