Perform glReadPixels with PBOs in the gpu, if PBOs are available.

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 <string>
 #include <vector>
 
@@ skipping 594 matching lines @@
 // back a GpuCommandBufferMsg_SignalSyncPointAck message with the same
 // signal_id.
 IPC_MESSAGE_ROUTED2(GpuCommandBufferMsg_SignalSyncPoint,
                     uint32 /* sync_point */,
                     uint32 /* signal_id */)
 
 // Response to GpuCommandBufferMsg_SignalSyncPoint.
 IPC_MESSAGE_ROUTED1(GpuCommandBufferMsg_SignalSyncPointAck,
                     uint32 /* signal_id */)
 
+// Makes this command buffer signal when a query is reached, by sending
+// back a GpuCommandBufferMsg_SignalSyncPointAck message with the same
+// signal_id.
+IPC_MESSAGE_ROUTED2(GpuCommandBufferMsg_SignalQuery,
+                    uint32 /* query */,
+                    uint32 /* signal_id */)
+
 //------------------------------------------------------------------------------
 // Accelerated Video Decoder Messages
 // These messages are sent from Renderer process to GPU process.
 
 // Send input buffer for decoding.
 IPC_MESSAGE_ROUTED3(AcceleratedVideoDecoderMsg_Decode,
                     base::SharedMemoryHandle, /* input_buffer_handle */
                     int32, /* bitstream_buffer_id */
                     uint32) /* size */
 
@@ skipping 47 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 */