Add comment to NavigationBodyLoader::OnReceiveCachedMetadata()

This function is used by the ServiceWorker, but is not covered by tests.
Add a comment to explain it is used.

Bug: None.
Change-Id: Iebf201e743debc01f16954e327f3abbe02f1bd40
Reviewed-on: https://chromium-review.googlesource.com/c/1455958
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630702}

content/renderer/loader/navigation_body_loader.cc

@@ -122,6 +122,11 @@ void NavigationBodyLoader::OnUploadProgress(int64_t current_position,
 
 void NavigationBodyLoader::OnReceiveCachedMetadata(
     const std::vector<uint8_t>& data) {
+  // Even if IsolatedCodeCaching is landed, this code is still used by
+  // ServiceWorker.
+  // TODO(horo, kinuko): Make a test to cover this function.
+  // TODO(https://crbug.com/930000): Add support for inline script code caching
+  // with the service worker service.
   client_->BodyCodeCacheReceived(data);
 }