diff -r 000000000000 -r 6474c204b198 ipc/chromium/src/base/id_map.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/ipc/chromium/src/base/id_map.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,105 @@
+// Copyright (c) 2006-2008 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 BASE_ID_MAP_H__
+#define BASE_ID_MAP_H__
+
+#include "base/basictypes.h"
+#include "base/hash_tables.h"
+#include "base/logging.h"
+
+// This object maintains a list of IDs that can be quickly converted to
+// pointers to objects. It is implemented as a hash table, optimized for
+// relatively small data sets (in the common case, there will be exactly one
+// item in the list).
+//
+// Items can be inserted into the container with arbitrary ID, but the caller
+// must ensure they are unique. Inserting IDs and relying on automatically
+// generated ones is not allowed because they can collide.
+template<class T>
+class IDMap {
+ private:
+  typedef base::hash_map<int32_t, T*> HashTable;
+  typedef typename HashTable::iterator iterator;
+
+ public:
+  // support const iterators over the items
+  // Note, use iterator->first to get the ID, iterator->second to get the T*
+  typedef typename HashTable::const_iterator const_iterator;
+
+  IDMap() : next_id_(1) {
+  }
+  IDMap(const IDMap& other) : next_id_(other.next_id_),
+                                        data_(other.data_) {
+  }
+
+  const_iterator begin() const {
+    return data_.begin();
+  }
+  const_iterator end() const {
+    return data_.end();
+  }
+
+  // Adds a view with an automatically generated unique ID. See AddWithID.
+  int32_t Add(T* data) {
+    int32_t this_id = next_id_;
+    DCHECK(data_.find(this_id) == data_.end()) << "Inserting duplicate item";
+    data_[this_id] = data;
+    next_id_++;
+    return this_id;
+  }
+
+  // Adds a new data member with the specified ID. The ID must not be in
+  // the list. The caller either must generate all unique IDs itself and use
+  // this function, or allow this object to generate IDs and call Add. These
+  // two methods may not be mixed, or duplicate IDs may be generated
+  void AddWithID(T* data, int32_t id) {
+    DCHECK(data_.find(id) == data_.end()) << "Inserting duplicate item";
+    data_[id] = data;
+  }
+
+  void Remove(int32_t id) {
+    iterator i = data_.find(id);
+    if (i == data_.end()) {
+      NOTREACHED() << "Attempting to remove an item not in the list";
+      return;
+    }
+    data_.erase(i);
+  }
+
+  bool IsEmpty() const {
+    return data_.empty();
+  }
+
+  void Clear() {
+    data_.clear();
+  }
+
+  bool HasData(const T* data) const {
+    // XXX would like to use <algorithm> here ...
+    for (const_iterator it = begin(); it != end(); ++it)
+      if (data == it->second)
+        return true;
+    return false;
+  }
+
+  T* Lookup(int32_t id) const {
+    const_iterator i = data_.find(id);
+    if (i == data_.end())
+      return NULL;
+    return i->second;
+  }
+
+  size_t size() const {
+    return data_.size();
+  }
+
+ protected:
+  // The next ID that we will return from Add()
+  int32_t next_id_;
+
+  HashTable data_;
+};
+
+#endif  // BASE_ID_MAP_H__