precache: Extract common methods for PrecacheManifest into util.

components/precache/core/precache_manifest_util.h

Index: components/precache/core/precache_manifest_util.h
diff --git a/components/precache/core/precache_manifest_util.h b/components/precache/core/precache_manifest_util.h
new file mode 100644
index 0000000000000000000000000000000000000000..b3e2ec2f55bc9bf15bbdc3fe2cf303a13307cfcd
--- /dev/null
+++ b/components/precache/core/precache_manifest_util.h
@@ -0,0 +1,30 @@
+// Copyright 2017 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.
+
+#ifndef COMPONENTS_PRECACHE_CORE_PRECACHE_MANIFEST_UTIL_H_
+#define COMPONENTS_PRECACHE_CORE_PRECACHE_MANIFEST_UTIL_H_
+
+#include <stdint.h>
+
+#include <vector>
+
+#include "base/optional.h"
+
+namespace precache {
+
+class PrecacheManifest;
+
+// Removes unknown fields from the |manifest| including embedded messages.
+void RemoveUnknownFields(PrecacheManifest* manifest);
+
+// Returns the resource selection bitset from the |manifest| for the given
+// |experiment_id|. If the experiment group is not found, then this returns
+// nullopt, in which case all resources should be selected.
+base::Optional<std::vector<bool>> GetResourceBitset(
+    const PrecacheManifest& manifest,
+    uint32_t experiment_id);
+
+}  // namespace precache
+
+#endif  // COMPONENTS_PRECACHE_CORE_PRECACHE_MANIFEST_UTIL_H_