Add logging for dup() failure in SharedMemoryHandle.

base/memory/shared_memory_handle_mac.cc

Index: base/memory/shared_memory_handle_mac.cc
diff --git a/base/memory/shared_memory_handle_mac.cc b/base/memory/shared_memory_handle_mac.cc
index 3f1d4d83748657a72366535c55aea37d077c3832..a440064a94500136af32ef2ddc5827513db4b125 100644
--- a/base/memory/shared_memory_handle_mac.cc
+++ b/base/memory/shared_memory_handle_mac.cc
@@ -9,6 +9,7 @@
 #include <sys/mman.h>
 #include <unistd.h>
 
+#include "base/logging.h"
 #include "base/mac/mac_util.h"
 #include "base/mac/mach_logging.h"
 #include "base/posix/eintr_wrapper.h"
@@ -69,8 +70,10 @@ SharedMemoryHandle SharedMemoryHandle::Duplicate() const {
       if (!IsValid())
         return SharedMemoryHandle();
       int duped_fd = HANDLE_EINTR(dup(file_descriptor_.fd));
-      if (duped_fd < 0)
+      if (duped_fd < 0) {
+        DPLOG(ERROR) << "dup() failed.";
         return SharedMemoryHandle();
+      }
       return SharedMemoryHandle(FileDescriptor(duped_fd, true));
     }
     case MACH: {