Use process_singleton_linux on Mac.

base/process/process_handle_mac.cc

Index: base/process/process_handle_mac.cc
diff --git a/base/process/process_handle_mac.cc b/base/process/process_handle_mac.cc
index 6cb8d686e4d77c1a605e6d18b5f0613fb398da90..cbf0bc5c4393fb9d3e0100e21ec3514ac504657b 100644
--- a/base/process/process_handle_mac.cc
+++ b/base/process/process_handle_mac.cc
@@ -4,6 +4,7 @@
 
 #include "base/process/process_handle.h"
 
+#include <libproc.h>
 #include <sys/sysctl.h>
 #include <sys/types.h>
 
@@ -24,4 +25,12 @@ ProcessId GetParentProcessId(ProcessHandle process) {
   return info.kp_eproc.e_ppid;
 }
 
+FilePath GetProcessExecutablePath(ProcessHandle process) {
+  char pathbuf[PROC_PIDPATHINFO_MAXSIZE];
+  if (!proc_pidpath(process, pathbuf, sizeof(pathbuf)))
+    return FilePath();
+
+  return FilePath(pathbuf);
+}
+
 }  // namespace base