Unify var tracking between webkit and the proxy.

ppapi/shared_impl/id_assignment.h

+// Copyright (c) 2011 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 PPAPI_SHARED_IMPL_ID_ASSIGNMENT_H_
+#define PPAPI_SHARED_IMPL_ID_ASSIGNMENT_H_
+
+#include <limits>
+
+#include "base/basictypes.h"
+
+namespace ppapi {
+
+enum PPIdType {
+  PP_ID_TYPE_MODULE,
+  PP_ID_TYPE_INSTANCE,
+  PP_ID_TYPE_RESOURCE,
+  PP_ID_TYPE_VAR,
+
+  // Not a real type, must be last.
+  PP_ID_TYPE_COUNT
+};
+
+extern const unsigned int kPPIdTypeBits;
+
+extern const int32 kMaxPPId;
+
+// The most significant bits are the type, the rest are the value.
+template <typename T> inline T MakeTypedId(T value, PPIdType type) {
+  return (value << kPPIdTypeBits) | static_cast<T>(type);
+}
+
+template <typename T> inline bool CheckIdType(T id, PPIdType type) {
+  // Say a resource of 0 is always valid, since that means "no resource."
+  // You shouldn't be passing 0 var, instance, or module IDs around so those
+  // are still invalid.
+  if (type == PP_ID_TYPE_RESOURCE && !id)
+    return true;
+  const T mask = (static_cast<T>(1) << kPPIdTypeBits) - 1;
+  return (id & mask) == type;
+}
+
+}  // namespace ppapi
+
+#endif  // PPAPI_SHARED_IMPL_ID_ASSIGNMENT_H_