Enable shared memory handle sharing in NaCl.

base/shared_memory_nacl.cc

Index: base/shared_memory_nacl.cc
diff --git a/base/shared_memory_nacl.cc b/base/shared_memory_nacl.cc
index fef293719ebc6b4898ac561d16f768b8d5f9366e..8d749867b49cc470b35ad7f7128cd35f593c97e6 100644
--- a/base/shared_memory_nacl.cc
+++ b/base/shared_memory_nacl.cc
@@ -137,7 +137,18 @@ void SharedMemory::Unlock() {
 bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
                                         SharedMemoryHandle *new_handle,
                                         bool close_self) {
-  return false;
+  const int new_fd = dup(mapped_file_);
+  if (new_fd < 0) {
+    DPLOG(ERROR) << "dup() failed.";
+    return false;
+  }
+
+  new_handle->fd = new_fd;
+  new_handle->auto_close = true;
+
+  if (close_self)
+    Close();
+  return true;
 }
 
 }  // namespace base