Make unknown extension subpermissions warnings instead of errors.

extensions/common/permissions/settings_override_permission.cc

Index: extensions/common/permissions/settings_override_permission.cc
diff --git a/extensions/common/permissions/settings_override_permission.cc b/extensions/common/permissions/settings_override_permission.cc
index b58d937d786ddbe5316387945a1b2545e1d597d3..63d8848fc4f126f76447ec3e9b5be8a6ee3ef753 100644
--- a/extensions/common/permissions/settings_override_permission.cc
+++ b/extensions/common/permissions/settings_override_permission.cc
@@ -64,8 +64,10 @@ bool SettingsOverrideAPIPermission::Equal(const APIPermission* rhs) const {
   return true;
 }
 
-bool SettingsOverrideAPIPermission::FromValue(const base::Value* value,
-                                              std::string* /*error*/) {
+bool SettingsOverrideAPIPermission::FromValue(
+    const base::Value* value,
+    std::string* /*error*/,
+    std::vector<std::string>* unhandled_permissions) {
   return (value == NULL);
 }