Declarative resource hints go through mojo IPC to //content

third_party/WebKit/public/platform/resource_hints.mojom

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module blink.mojom;
+
+import "url/mojo/url.mojom";
+
+// The ResourceHintsDispatcherHost sends preconnect/preresolve requests based
+// on link tags/headers. See the corresponding interface in
+// content/public/resource_hints.h.
+// TODO(csharrison): Extend this interface to include page scans and link hovers.
+interface ResourceHintsDispatcherHost {
+  DispatchPreconnect(url.mojom.Url url, bool credentials_flag, uint8 num_connections);
+  DispatchPreresolve(url.mojom.Url url);
+};