Delay UpdateRect until the SwapBuffers callback when accelerated compositing is on.

content/browser/renderer_host/render_widget_host.cc

Index: content/browser/renderer_host/render_widget_host.cc
diff --git a/content/browser/renderer_host/render_widget_host.cc b/content/browser/renderer_host/render_widget_host.cc
index 404ff86093ef97319b1da921c70cda7dfbc631d1..461de1cc69230896df8ec57b9a03b5c8726be9cc 100644
--- a/content/browser/renderer_host/render_widget_host.cc
+++ b/content/browser/renderer_host/render_widget_host.cc
@@ -195,6 +195,7 @@ bool RenderWidgetHost::OnMessageReceived(const IPC::Message &msg) {
     IPC_MESSAGE_HANDLER(ViewHostMsg_SetTooltipText, OnMsgSetTooltipText)
     IPC_MESSAGE_HANDLER(ViewHostMsg_PaintAtSize_ACK, OnMsgPaintAtSizeAck)
     IPC_MESSAGE_HANDLER(ViewHostMsg_UpdateRect, OnMsgUpdateRect)
+    IPC_MESSAGE_HANDLER(ViewHostMsg_UpdateIsDelayed, OnMsgUpdateIsDelayed)
     IPC_MESSAGE_HANDLER(ViewHostMsg_HandleInputEvent_ACK, OnMsgInputEventAck)
     IPC_MESSAGE_HANDLER(ViewHostMsg_Focus, OnMsgFocus)
     IPC_MESSAGE_HANDLER(ViewHostMsg_Blur, OnMsgBlur)
@@ -1036,17 +1037,23 @@ void RenderWidgetHost::OnMsgUpdateRect(
   UMA_HISTOGRAM_TIMES("MPArch.RWH_OnMsgUpdateRect", delta);
 }
 
+void RenderWidgetHost::OnMsgUpdateIsDelayed() {
+  // Nothing to do, this message was just to unblock the UI thread.
+}
+
 void RenderWidgetHost::DidUpdateBackingStore(
     const ViewHostMsg_UpdateRect_Params& params,
     const TimeTicks& paint_start) {
   TRACE_EVENT0("renderer_host", "RenderWidgetHost::DidUpdateBackingStore");
   TimeTicks update_start = TimeTicks::Now();
 
-  // ACK early so we can prefetch the next PaintRect if there is a next one.
-  // This must be done AFTER we're done painting with the bitmap supplied by the
-  // renderer. This ACK is a signal to the renderer that the backing store can
-  // be re-used, so the bitmap may be invalid after this call.
-  Send(new ViewMsg_UpdateRect_ACK(routing_id_));
+  if (ViewHostMsg_UpdateRect_Flags::needs_ack(params.flags)) {
+      // ACK early so we can prefetch the next PaintRect if there is a next one.

[darin (slow to review), 2011/11/15 08:06:04]

nit: indentation

[piman, 2011/11/16 01:00:55]

Done.

+      // This must be done AFTER we're done painting with the bitmap supplied by
+      // the renderer. This ACK is a signal to the renderer that the backing
+      // store can be re-used, so the bitmap may be invalid after this call.
+      Send(new ViewMsg_UpdateRect_ACK(routing_id_));
+  }
 
   // Move the plugins if the view hasn't already been destroyed.  Plugin moves
   // will not be re-issued, so must move them now, regardless of whether we