Free the command buffer when tabs are switched

gpu/command_buffer/client/cmd_buffer_helper.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.
 
 // This file contains the command buffer helper class.
 
 #ifndef GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_
 #define GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_
 
 #include <string.h>
@@ skipping 200 matching lines @@
   }
 
   CommandBuffer* command_buffer() const {
     return command_buffer_;
   }
 
   Buffer get_ring_buffer() const {
     return ring_buffer_;
   }
 
+  void FreeRingBuffer();
+
+  bool HaveRingBuffer() const {
+    return ring_buffer_id_ != -1;
+  }
+
  private:
   // Waits until get changes, updating the value of get_.
   void WaitForGetChange();
 
   // Returns the number of available entries (they may not be contiguous).
   int32 AvailableEntries() {
     return (get_offset() - put_ - 1 + usable_entry_count_) %
         usable_entry_count_;
   }
 
@@ skipping 14 matching lines @@
   // Using C runtime instead of base because this file cannot depend on base.
   clock_t last_flush_time_;
 
   friend class CommandBufferHelperTest;
   DISALLOW_COPY_AND_ASSIGN(CommandBufferHelper);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_CMD_BUFFER_HELPER_H_