[WIP] [url_utils] Implement a contiguous SchemeSet to replace vector<SchemeWithType>

url/scheme_set.cc

+// 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.
+
+#include "url/scheme_set.h"
+
+namespace url {
+
+SchemeSet::SchemeSet() {}
+SchemeSet::~SchemeSet() {}
+
+void SchemeSet::add(const char* scheme) {
+  size_t len = backing_string_.size();
+  backing_string_.append(scheme);
+  size_t delta = backing_string_.size() - len;
+  pieces_.emplace_back(len, delta);
+}
+
+}  // namespace url