Add RoutingIDIssuer to ensure the correctness of ID to be routed.

content/browser/renderer_host/routing_id_issuer.cc

+// Copyright (c) 2012 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 "content/browser/renderer_host/routing_id_issuer.h"
+
+namespace content {
+
+namespace {
+
+const int kManglerBits = 3;
+const int kIDBits = 31 - kManglerBits;
+const int kManglerWrap = 1 << kManglerBits;
+const int kIDWrap = 1 << kIDBits;
+const int kIDMask = kIDWrap - 1;
+
+static base::StaticAtomicSequenceNumber g_manglerSequence;
+static int g_disablingIDManglingCount = 0;
+
+int GetNextMangler() {
+  // Does +1 to always gives some mangler.
+  return (g_manglerSequence.GetNext() % (kManglerWrap - 1)) + 1;
+}
+
+}  // namespace
+
+scoped_ptr<RoutingIDIssuer> RoutingIDIssuer::Create() {
+  if (0 < g_disablingIDManglingCount)
+    return make_scoped_ptr(new RoutingIDIssuer(0));
+
+  DCHECK(0 == g_disablingIDManglingCount);
+  return make_scoped_ptr(new RoutingIDIssuer(GetNextMangler()));
+}
+
+scoped_ptr<RoutingIDIssuer> RoutingIDIssuer::CreateWithMangler(int mangler) {
+  return make_scoped_ptr(new RoutingIDIssuer(mangler));
+}
+
+RoutingIDIssuer::RoutingIDIssuer(int mangler) : mangler_(mangler) {
+  DCHECK(0 <= mangler_ && mangler_ < kManglerWrap) << mangler_
+                                                   << ">=" << kManglerWrap;
+}
+
+int RoutingIDIssuer::IssueNext() {
+  return (mangler_ << kIDBits) | ((next_.GetNext() + 1) & kIDMask);
+}
+
+bool RoutingIDIssuer::IsProbablyValid(int issued_id) const {
+  return (mangler_ << kIDBits) == (issued_id & ~kIDMask);
+}
+
+void RoutingIDIssuer::DisableIDMangling() {
+  g_disablingIDManglingCount++;
+}
+
+void RoutingIDIssuer::EnableIDMangling() {
+  g_disablingIDManglingCount--;
+  DCHECK(0 <= g_disablingIDManglingCount);
+}
+
+}  // namespace content