Organize Layout Hooks (content-side).

content/common/view_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.
 
 // IPC messages for page rendering.
 // Multiply-included message file, hence no include guard.
 
 #include "base/memory/shared_memory.h"
 #include "base/process/process.h"
 #include "base/strings/string16.h"
@@ skipping 1496 matching lines @@
 
 // Message sent from the renderer to the browser when a HTML form validation
 // message should be hidden from view.
 IPC_MESSAGE_ROUTED0(ViewHostMsg_HideValidationMessage)
 
 // Message sent from the renderer to the browser when the suggested co-ordinates
 // of the anchor for a HTML form validation message have changed.
 IPC_MESSAGE_ROUTED1(ViewHostMsg_MoveValidationMessage,
                     gfx::Rect /* anchor rectangle in root view coordinate */)
 
+// Sent once a paint happens after the first non empty layout. In other words
+// after the frame has painted something.

[dcheng, 2015/08/31 16:46:01]

"frame" -> "frame widget"? Not sure what the best terminology for the comment
is.

+IPC_MESSAGE_ROUTED0(ViewHostMsg_DidFirstVisuallyNonEmptyPaint)
+
 #if defined(OS_ANDROID)
 // Response to ViewMsg_FindMatchRects.
 //
 // |version| will contain the current version number of the renderer's find
 // match list (incremented whenever they change), which should be passed in the
 // next call to ViewMsg_FindMatchRects.
 //
 // |rects| will either contain a list of the enclosing rects of all matches
 // found by the most recent Find operation, or will be empty if |version| is not
 // greater than the |current_version| passed to ViewMsg_FindMatchRects (hence
@@ skipping 58 matching lines @@
 // cached by the OS. Please see RenderMessageFilter::OnPreCacheFontCharacters
 // for details.
 IPC_SYNC_MESSAGE_CONTROL2_0(ViewHostMsg_PreCacheFontCharacters,
                             LOGFONT /* font_data */,
                             base::string16 /* characters */)
 #endif
 
 // Adding a new message? Stick to the sort order above: first platform
 // independent ViewMsg, then ifdefs for platform specific ViewMsg, then platform
 // independent ViewHostMsg, then ifdefs for platform specific ViewHostMsg.