Fix loading placeholders for Lo-Fi

content/browser/web_contents/web_contents_impl.cc

 // 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.
 
 #include "content/browser/web_contents/web_contents_impl.h"
 
 #include <stddef.h>
 
 #include <cmath>
 #include <utility>
@@ skipping 2541 matching lines @@
 void WebContentsImpl::ReloadFocusedFrame(bool bypass_cache) {
   RenderFrameHost* focused_frame = GetFocusedFrame();
   if (!focused_frame)
     return;
 
   focused_frame->Send(new FrameMsg_Reload(
       focused_frame->GetRoutingID(), bypass_cache));
 }
 
 void WebContentsImpl::ReloadLoFiImages() {
+  // Lo-Fi images must first be disabled synchronously so new frames are not
+  // created with Lo-Fi enabled.
+  SendToAllFrames(new FrameMsg_DisableLoFiImages(MSG_ROUTING_NONE));

[clamy, 2016/07/07 15:16:30]

I'm not sure this works with PlzNavigate enabled. Do you also want to disable
LoFi for any ongoing navigation in the WebContents? In this case, with
PlzNavigate enabled there's probably some extra-work to do.

[megjablon, 2016/07/07 19:31:52]

Will didCommitProvisionalLoad be called later for the main frame with
PlzNavigate? That's the only place we update the main frame's Lo-Fi state from
an external value. Otherwise, every subframe inherits the parent frame's state
and the only way we can change that is through the DisableLoFiImages call.

I tried to test with --enable-browser-side-navigation, but origin/master has a
crash with the flag:

resource_prefetch_common.cc(176)] Check failed: is_valid() && rhs.is_valid(). 

[clamy, 2016/07/08 14:46:26]

Well if you have a navigation that's ongoing we can call didCommitProvisional
for the main frame after we send these IPCs. That said, this would result in a
document change, so previous LoFi images will go away (but the new document may
be using lofi). What's the behavior supposed to be in that case?

Normally there should be no issue with content_browsertests & content_unittests
using PlzNavigate (except if using ServiceWorker). Chrome layer might have
issues though.

   SendToAllFrames(new FrameMsg_ReloadLoFiImages(MSG_ROUTING_NONE));
 }
 
 void WebContentsImpl::Undo() {
   RenderFrameHost* focused_frame = GetFocusedFrame();
   if (!focused_frame)
     return;
 
   focused_frame->Send(new InputMsg_Undo(focused_frame->GetRoutingID()));
   RecordAction(base::UserMetricsAction("Undo"));
@@ skipping 2589 matching lines @@
   for (RenderViewHost* render_view_host : render_view_host_set)
     render_view_host->OnWebkitPreferencesChanged();
 }
 
 void WebContentsImpl::SetJavaScriptDialogManagerForTesting(
     JavaScriptDialogManager* dialog_manager) {
   dialog_manager_ = dialog_manager;
 }
 
 }  // namespace content