Add in-profile external_extensions.json file for Chrome OS OEM customization.

chrome/common/chrome_paths.cc

Index: chrome/common/chrome_paths.cc
diff --git a/chrome/common/chrome_paths.cc b/chrome/common/chrome_paths.cc
index 51aa0191d067a407eff0621949c2a734589ffb71..957c83fb4320548701b08a5e8440181f887b6288 100644
--- a/chrome/common/chrome_paths.cc
+++ b/chrome/common/chrome_paths.cc
@@ -320,6 +320,14 @@ bool PathProvider(int key, FilePath* result) {
       break;
     }
 #endif
+#if defined(OS_CHROMEOS)
+    case chrome::DIR_USER_EXTERNAL_EXTENSIONS: {
+      if (!PathService::Get(chrome::DIR_USER_DATA, &cur))
+        return false;
+      cur = cur.Append(FILE_PATH_LITERAL("External Extensions"));
+      break;
+    }
+#endif
     default:
       return false;
   }