Make unknown extension subpermissions warnings instead of errors.

extensions/common/permissions/media_galleries_permission.cc

Index: extensions/common/permissions/media_galleries_permission.cc
diff --git a/extensions/common/permissions/media_galleries_permission.cc b/extensions/common/permissions/media_galleries_permission.cc
index baf71624b45d3618d27087782bac579a80454bf8..1d7838a1f63eabf4d7c2b0ebf90811f1a0d6234a 100644
--- a/extensions/common/permissions/media_galleries_permission.cc
+++ b/extensions/common/permissions/media_galleries_permission.cc
@@ -56,14 +56,25 @@ MediaGalleriesPermission::MediaGalleriesPermission(
 MediaGalleriesPermission::~MediaGalleriesPermission() {
 }
 
-bool MediaGalleriesPermission::FromValue(const base::Value* value,
-                                         std::string* error) {
+bool MediaGalleriesPermission::FromValue(
+    const base::Value* value,
+    std::string* error,
+    std::vector<std::string>* unhandled_permissions) {
+  std::vector<std::string> unhandled_sub_permissions;
   if (!SetDisjunctionPermission<MediaGalleriesPermissionData,
-                                MediaGalleriesPermission>::FromValue(value,
-                                                                     error)) {
+                                MediaGalleriesPermission>::FromValue(
+                                    value, error, &unhandled_sub_permissions)) {
+    unhandled_permissions->insert(unhandled_permissions->end(),
+                                  unhandled_sub_permissions.begin(),
+                                  unhandled_sub_permissions.end());
     return false;
   }
 
+  for (size_t i = 0; i < unhandled_sub_permissions.size(); i++) {
+    unhandled_permissions->push_back(
+        "{\"mediaGalleries\": [" + unhandled_sub_permissions[i] + "]}");
+  }
+
   bool has_read = false;
   bool has_copy_to = false;
   bool has_delete = false;