Add logging for dup() failure in SharedMemoryHandle.

base/memory/shared_memory_handle_posix.cc

Index: base/memory/shared_memory_handle_posix.cc
diff --git a/base/memory/shared_memory_handle_posix.cc b/base/memory/shared_memory_handle_posix.cc
index 3e9a403b14c23f8700cbf4105632c661edd6c6dc..2d230786fa85257c7d4d10497f5839208cb1cdb5 100644
--- a/base/memory/shared_memory_handle_posix.cc
+++ b/base/memory/shared_memory_handle_posix.cc
@@ -57,8 +57,10 @@ SharedMemoryHandle SharedMemoryHandle::Duplicate() const {
     return SharedMemoryHandle();
 
   int duped_handle = HANDLE_EINTR(dup(file_descriptor_.fd));
-  if (duped_handle < 0)
+  if (duped_handle < 0) {
+    DPLOG(ERROR) << "dup() failed.";
     return SharedMemoryHandle();
+  }
   return SharedMemoryHandle(FileDescriptor(duped_handle, true));
 }