prefs: use system-provided preference skeleton

This patch makes it possible for distributions to have a global
default preferences file in /etc/iridium-browser/preferences that get
copied over to ~ when the user starts the program for the first time.

chrome/browser/first_run/first_run_internal_linux.cc

@@ -20,8 +20,12 @@ bool IsOrganicFirstRun() {
 base::FilePath MasterPrefsPath() {
   // The standard location of the master prefs is next to the chrome binary.
   base::FilePath master_prefs;
+#ifndef ANDROID
+  master_prefs = base::FilePath("/etc/iridium-browser");
+#else
   if (!base::PathService::Get(base::DIR_EXE, &master_prefs))
     return base::FilePath();
+#endif
   return master_prefs.AppendASCII(installer::kDefaultMasterPrefs);
 }