Added GPU process "echo" IPC message.

content/renderer/gpu/command_buffer_proxy.cc

Index: content/renderer/gpu/command_buffer_proxy.cc
===================================================================
--- content/renderer/gpu/command_buffer_proxy.cc	(revision 98655)
+++ content/renderer/gpu/command_buffer_proxy.cc	(working copy)
@@ -8,6 +8,7 @@
 #include "base/logging.h"
 #include "base/process_util.h"
 #include "base/shared_memory.h"
+#include "base/stl_util.h"
 #include "base/task.h"
 #include "content/common/gpu/gpu_messages.h"
 #include "content/common/plugin_messages.h"
@@ -45,9 +46,9 @@
   IPC_BEGIN_MESSAGE_MAP(CommandBufferProxy, message)
     IPC_MESSAGE_HANDLER(GpuCommandBufferMsg_UpdateState, OnUpdateState);
     IPC_MESSAGE_HANDLER(GpuCommandBufferMsg_Destroyed, OnDestroyed);
-    IPC_MESSAGE_HANDLER(GpuCommandBufferMsg_SwapBuffers, OnSwapBuffers);
     IPC_MESSAGE_HANDLER(GpuCommandBufferMsg_NotifyRepaint,
                         OnNotifyRepaint);
+    IPC_MESSAGE_HANDLER(GpuCommandBufferMsg_EchoAck, OnEchoAck);
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
 
@@ -79,6 +80,13 @@
   }
 }
 
+void CommandBufferProxy::OnEchoAck() {
+  DCHECK(!echo_tasks_.empty());
+  Task* task = echo_tasks_.front().release();
+  echo_tasks_.pop();
+  task->Run();
+}
+
 void CommandBufferProxy::SetChannelErrorCallback(Callback0::Type* callback) {
   channel_error_callback_.reset(callback);
 }
@@ -344,9 +352,20 @@
   NOTREACHED();
 }
 
-void CommandBufferProxy::OnSwapBuffers() {
-  if (swap_buffers_callback_.get())
-    swap_buffers_callback_->Run();
+bool CommandBufferProxy::Echo(Task* task) {
+  if (last_state_.error != gpu::error::kNoError) {
+    delete task;
+    return false;
+  }
+
+  if (!Send(new GpuChannelMsg_Echo(GpuCommandBufferMsg_EchoAck(route_id_)))) {
+    delete task;
+    return false;
+  }
+
+  echo_tasks_.push(linked_ptr<Task>(task));
+
+  return true;
 }
 
 bool CommandBufferProxy::SetParent(CommandBufferProxy* parent_command_buffer,
@@ -376,10 +395,6 @@
   return result;
 }
 
-void CommandBufferProxy::SetSwapBuffersCallback(Callback0::Type* callback) {
-  swap_buffers_callback_.reset(callback);
-}
-
 void CommandBufferProxy::SetNotifyRepaintTask(Task* task) {
   notify_repaint_task_.reset(task);
 }