Adding logic to prevent offline previews fallback to LoFi/Weblite

chrome/browser/previews/previews_infobar_delegate.cc

 // Copyright 2016 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 "chrome/browser/previews/previews_infobar_delegate.h"
 
 #include "base/metrics/histogram_macros.h"
 #include "chrome/browser/android/android_theme_resources.h"
 #include "chrome/browser/infobars/infobar_service.h"
 #include "chrome/browser/net/spdyproxy/data_reduction_proxy_chrome_settings.h"
@@ skipping 137 matching lines @@
       web_contents->GetController().Reload(
           content::ReloadType::DISABLE_LOFI_MODE, true);
     else if (infobar_type_ == LOFI)
       web_contents->ReloadLoFiImages();
 
     auto* data_reduction_proxy_settings =
         DataReductionProxyChromeSettingsFactory::GetForBrowserContext(
             web_contents->GetBrowserContext());
     data_reduction_proxy_settings->IncrementLoFiUserRequestsForImages();
   } else if (infobar_type_ == OFFLINE) {
-    web_contents->GetController().Reload(content::ReloadType::NORMAL, true);
+    web_contents->GetController().Reload(content::ReloadType::DISABLE_LOFI_MODE,

[bengr, 2017/03/31 16:59:56]

Does this flag also disable lite pages? If so, please file a bug to change the
name to DISABLE_SERVER_PREVIEWS, or something like that. If not, please explain
how this covers lite pages.

Also, please explain how the following is prevented:
1) a lite page is fetched, because there wasn't an offline page
2) an offline page is created from the lite page
3) the user selects show original and gets the offline page.

Add a test please.

[RyanSturm, 2017/03/31 18:53:42]

DISABLE_LOFI_MODE triggers PREVIEWS_NO_TRANSFORM, which prevents any server
transform for requests on the page.
Is this a problem? If this were a problem, I'd think there would need to be
special logic preventing the user from off-lining any weblite preview, which
seems like a valid use case. Is there a particular case where this causes a
problem? With the regularity of the offline page logic changing perhaps they
should be aware that automatically offlining a page is not a good idea when a
preview is showing.
Offline previews are not show on *any* reload.
I added a test to verify that DISABLE_LOFI_MODE is added for this case. a
browser test checks that this flag does the right thing:
https://cs.chromium.org/chromium/src/content/browser/loader/resource_dispatch...

+                                         true);
   }
 
   return true;
 }