Pass a sequence number along with the DIB handle when compositing in software.

ui/surface/transport_dib.h

 // 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.
 
 #ifndef UI_SURFACE_TRANSPORT_DIB_H_
 #define UI_SURFACE_TRANSPORT_DIB_H_
 
 #include "base/basictypes.h"
 #include "ui/surface/surface_export.h"
 
@@ skipping 36 matching lines @@
     HandleAndSequenceNum()
         : handle(NULL),
           sequence_num(0) {
     }
 
     HandleAndSequenceNum(HANDLE h, uint32 seq_num)
         : handle(h),
           sequence_num(seq_num) {
     }
 
+    bool operator==(const HandleAndSequenceNum& other) const {
+      return other.handle == handle && other.sequence_num == sequence_num;
+    }
+
     bool operator<(const HandleAndSequenceNum& other) const {
       // Use the lexicographic order on the tuple <handle, sequence_num>.
       if (other.handle != handle)
         return other.handle < handle;
       return other.sequence_num < sequence_num;
     }
 
     HANDLE handle;
     uint32 sequence_num;
   };
@@ skipping 153 matching lines @@
   Display* display_;  // connection to the X server
   size_t inflight_counter_;  // How many requests to the X server are in flight
   bool detached_;  // If true, delete the transport DIB when it is idle
 #endif
   size_t size_;  // length, in bytes
 
   DISALLOW_COPY_AND_ASSIGN(TransportDIB);
 };
 
 #endif  // UI_SURFACE_TRANSPORT_DIB_H_