Mojo: Make room for remotely-allocated channel endpoint IDs.

mojo/edk/system/channel_endpoint_id.cc

 // Copyright 2014 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 "mojo/edk/system/channel_endpoint_id.h"
 
+#include "base/compiler_specific.h"
+
 namespace mojo {
 namespace system {
 
+STATIC_CONST_MEMBER_DEFINITION const uint32_t
+    ChannelEndpointId::kRemotelyAllocatedFlag;
+STATIC_CONST_MEMBER_DEFINITION const uint32_t
+    ChannelEndpointId::kLocallyAllocatedMask;
+
 ChannelEndpointId LocalChannelEndpointIdGenerator::GetNext() {
   ChannelEndpointId rv = next_channel_endpoint_id_;
-  next_channel_endpoint_id_.value_++;
+  next_channel_endpoint_id_.value_ = (next_channel_endpoint_id_.value_ + 1) &
+                                     ChannelEndpointId::kLocallyAllocatedMask;
   // Skip over the invalid value, in case we wrap.
   if (!next_channel_endpoint_id_.is_valid())
     next_channel_endpoint_id_.value_++;
   return rv;
 }
 
 }  // namespace system
 }  // namespace mojo