Allow gpu ringbuffer to wrap around.

gpu/command_buffer/client/ring_buffer.h

 // Copyright (c) 2010 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 definition of the RingBuffer class.
 
 #ifndef GPU_COMMAND_BUFFER_CLIENT_RING_BUFFER_H_
 #define GPU_COMMAND_BUFFER_CLIENT_RING_BUFFER_H_
 
 #include <deque>
@@ skipping 43 matching lines @@
   unsigned int GetLargestFreeSizeNoWaiting();
 
   // Gets the size of the largest free block that can be allocated if the
   // caller can wait. Allocating a block of this size will succeed, but may
   // block.
   unsigned int GetLargestFreeOrPendingSize() {
     return size_;
   }
 
  private:
+  enum State {
+    IN_USE,
+    PADDING,
+    FREE_PENDING_TOKEN
+  };
   // Book-keeping sturcture that describes a block of memory.
   struct Block {
-    Block(Offset _offset, unsigned int _size)
+    Block(Offset _offset, unsigned int _size, State _state)
         : offset(_offset),
           size(_size),
           token(0),
-          valid(false) {
+          state(_state) {
     }
     Offset offset;
     unsigned int size;
     unsigned int token;  // token to wait for.
-    bool valid;  // whether or not token has been set.
+    State state;
   };
 
   typedef std::deque<Block> Container;
   typedef unsigned int BlockIndex;
 
   void FreeOldestBlock();
 
   CommandBufferHelper* helper_;
 
   // Used blocks are added to the end, blocks are freed from the beginning.
@@ skipping 97 matching lines @@
  private:
   RingBuffer allocator_;
   void* base_;
   RingBuffer::Offset base_offset_;
   DISALLOW_IMPLICIT_CONSTRUCTORS(RingBufferWrapper);
 };
 
 }  // namespace gpu
 
 #endif  // GPU_COMMAND_BUFFER_CLIENT_RING_BUFFER_H_