Use shared memory to update the renderer's view of the command buffer state.

content/common/gpu/gpu_messages.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.
 
 // Multiply-included message file, hence no include guard here, but see below
 // for a much smaller-than-usual include guard section.
 
 #include <vector>
 #include <string>
 
@@ skipping 300 matching lines @@
 //------------------------------------------------------------------------------
 // GPU Command Buffer Messages
 // These are messages between a renderer process to the GPU process relating to
 // a single OpenGL context.
 // Initialize a command buffer with the given number of command entries.
 // Returns the shared memory handle for the command buffer mapped to the
 // calling process.
 IPC_SYNC_MESSAGE_ROUTED0_1(GpuCommandBufferMsg_Initialize,
                            bool /* result */)
 
+// Sets the shared memory buffer used to hold the CommandBufferSharedState,
+// used to transmit the current state.
+IPC_SYNC_MESSAGE_ROUTED1_0(GpuCommandBufferMsg_SetSharedStateBuffer,
+                           int32 /* shm_id */)
+
 // Sets the shared memory buffer used for commands.
 IPC_SYNC_MESSAGE_ROUTED1_0(GpuCommandBufferMsg_SetGetBuffer,
                            int32 /* shm_id */)
 
 // Sets the parent command buffer. This allows the parent and child to share
 // textures.
 IPC_SYNC_MESSAGE_ROUTED2_1(GpuCommandBufferMsg_SetParent,
                            int32 /* parent_route_id */,
                            uint32 /* parent_texture_id */,
                            bool /* result */)
 
 // Get the current state of the command buffer.
 IPC_SYNC_MESSAGE_ROUTED0_1(GpuCommandBufferMsg_GetState,
                            gpu::CommandBuffer::State /* state */)
 
 // Get the current state of the command buffer, as fast as possible.
 IPC_SYNC_MESSAGE_ROUTED0_1(GpuCommandBufferMsg_GetStateFast,
                            gpu::CommandBuffer::State /* state */)
 
 // Asynchronously synchronize the put and get offsets of both processes.
 // Caller passes its current put offset. Current state (including get offset)
-// is returned via an UpdateState message.
+// is returned in shared memory.
 IPC_MESSAGE_ROUTED2(GpuCommandBufferMsg_AsyncFlush,
                     int32 /* put_offset */,
                     uint32 /* flush_count */)
 
 // Asynchronously process any commands known to the GPU process. This is only
 // used in the event that a channel is unscheduled and needs to be flushed
 // again to process any commands issued subsequent to unscheduling. The GPU
 // process actually sends it (deferred) to itself.
 IPC_MESSAGE_ROUTED0(GpuCommandBufferMsg_Rescheduled)
 
-// Return the current state of the command buffer following a request via
-// an AsyncGetState or AsyncFlush message. (This message is sent from the
-// GPU process to the renderer process.)
-IPC_MESSAGE_ROUTED1(GpuCommandBufferMsg_UpdateState,
-                    gpu::CommandBuffer::State /* state */)
-
 // Sent by the GPU process to display messages in the console.
 IPC_MESSAGE_ROUTED1(GpuCommandBufferMsg_ConsoleMsg,
                     GPUCommandBufferConsoleMessage /* msg */)
 
 // Create a shared memory transfer buffer. Returns an id that can be used to
 // identify the transfer buffer from a comment.
 IPC_SYNC_MESSAGE_ROUTED2_1(GpuCommandBufferMsg_CreateTransferBuffer,
                            int32 /* size */,
                            int32 /* id_request (-1 means any) */,
                            int32 /* id */)
@@ skipping 112 matching lines @@
 
 // Confirm decoder has been flushed.
 IPC_MESSAGE_ROUTED0(AcceleratedVideoDecoderHostMsg_FlushDone)
 
 // Confirm decoder has been reset.
 IPC_MESSAGE_ROUTED0(AcceleratedVideoDecoderHostMsg_ResetDone)
 
 // Video decoder has encountered an error.
 IPC_MESSAGE_ROUTED1(AcceleratedVideoDecoderHostMsg_ErrorNotification,
                     uint32) /* Error ID */