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

content/common/view_message_enums.h

 // Copyright (c) 2011 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.
 
 #ifndef CONTENT_COMMON_VIEW_MESSAGES_ENUMS_H_
 #define CONTENT_COMMON_VIEW_MESSAGES_ENUMS_H_
 
 struct ViewHostMsg_AccEvent {
   enum Value {
     // The active descendant of a node has changed.
@@ skipping 85 matching lines @@
   };
 };
 
 // Values that may be OR'd together to form the 'flags' parameter of a
 // ViewHostMsg_UpdateRect_Params structure.
 struct ViewHostMsg_UpdateRect_Flags {
   enum {
     IS_RESIZE_ACK = 1 << 0,
     IS_RESTORE_ACK = 1 << 1,
     IS_REPAINT_ACK = 1 << 2,
+    NEEDS_ACK = 1 << 3,
   };
   static bool is_resize_ack(int flags) {
     return (flags & IS_RESIZE_ACK) != 0;
   }
   static bool is_restore_ack(int flags) {
     return (flags & IS_RESTORE_ACK) != 0;
   }
   static bool is_repaint_ack(int flags) {
     return (flags & IS_REPAINT_ACK) != 0;
   }
+  static bool needs_ack(int flags) {

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

it seems a bit awkward to put this flag here.  the above three bits are
indicating that a ViewHostMsg_UpdateRect IPC is in response to a Resize, Restore
or Repaint request made by the browser.  here, needs_ack is saying whether an
UpdateRect_ACK message should be sent in reply to the UpdateRect message.  this
ack has nothing to do with the other acks.

this perhaps suggests that needs_ack should really be part of the
UpdateRect_Params structure as a boolean member.

counterargument:  this member of UpdateRect_Params is named "flags", which is a
very generic sounding field.  that naming seems to welcome putting other bits in
as flags as you have done.  so perhaps i'm a bit torn.  it took me a while to
mentally separate the IS_{RESIZE,RESTORE,REPAINT}_ACK bits from the NEEDS_ACK
bits.  they are completely unrelated and yet look like they must be related :-(

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

Done.

+    return (flags & NEEDS_ACK) != 0;
+  }
 };
 
 struct ViewMsg_Navigate_Type {
  public:
   enum Value {
     // Reload the page.
     RELOAD,
 
     // Reload the page, ignoring any cache entries.
     RELOAD_IGNORING_CACHE,
@@ skipping 19 matching lines @@
     kActivateSelection
   };
 
   ViewMsg_StopFinding_Params() : action(kClearSelection) {}
 
   // The action that should be taken when the find is completed.
   Action action;
 };
 
 #endif  // CONTENT_COMMON_VIEW_MESSAGES_ENUMS_H_