Fix loading placeholders for Lo-Fi

content/common/frame_messages.h

 // Copyright 2013 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 interacting with frames.
 // Multiply-included message file, hence no include guard.
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 618 matching lines @@
 
 // Notifies the embedding frame that the process rendering the child frame's
 // contents has terminated.
 IPC_MESSAGE_ROUTED0(FrameMsg_ChildFrameProcessGone)
 
 // Sent in response to a FrameHostMsg_ContextMenu to let the renderer know that
 // the menu has been closed.
 IPC_MESSAGE_ROUTED1(FrameMsg_ContextMenuClosed,
                     content::CustomContextMenuContext /* custom_context */)
 
+// Disables loading Lo-Fi images in the RenderFrame.
+IPC_SYNC_MESSAGE_ROUTED0_0(FrameMsg_DisableLoFiImages)

[nasko, 2016/07/12 19:03:57]

Why is this a sync message? Sync messages should never be sent from the browser
to the renderer, as it allows any malicious renderer to hang the entire browser.

[Charlie Reis, 2016/07/12 19:17:06]

It also makes deadlock possible, because the renderer can be sending sync IPCs
to the browser at the same time.

+
 // Reloads all the Lo-Fi images in the RenderFrame. Ignores the cache and
 // reloads from the network.
 IPC_MESSAGE_ROUTED0(FrameMsg_ReloadLoFiImages)
 
 // Executes custom context menu action that was provided from Blink.
 IPC_MESSAGE_ROUTED2(FrameMsg_CustomContextMenuAction,
                     content::CustomContextMenuContext /* custom_context */,
                     unsigned /* action */)
 
 // Requests that the RenderFrame or RenderFrameProxy updates its opener to the
@@ skipping 930 matching lines @@
 // nearest find result in the sending frame.
 IPC_MESSAGE_ROUTED2(FrameHostMsg_GetNearestFindResult_Reply,
                     int /* nfr_request_id */,
                     float /* distance */)
 #endif
 
 // Adding a new message? Stick to the sort order above: first platform
 // independent FrameMsg, then ifdefs for platform specific FrameMsg, then
 // platform independent FrameHostMsg, then ifdefs for platform specific
 // FrameHostMsg.