Fix loading placeholders for Lo-Fi

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 23a03d9b75fac5e2fd7bb91fa7001bfe8296fbcc..b0af69ed31a6fc3f5c2f9b10121abec6cb09cad4 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -2559,6 +2559,9 @@ void WebContentsImpl::ReloadFocusedFrame(bool 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));
 }