[iOS Reading List] Add distilling WKWebView to the view hierarchy.

ios/chrome/browser/reading_list/reading_list_distiller_page.mm

 // 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 "ios/chrome/browser/reading_list/reading_list_distiller_page.h"
 
 #include "base/bind.h"
 #include "base/mac/foundation_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ skipping 54 matching lines @@
   if (old_web_state) {
     web_state_dispatcher_->ReturnWebState(std::move(old_web_state));
   }
   std::unique_ptr<web::WebState> new_web_state =
       web_state_dispatcher_->RequestWebState();
   AttachWebState(std::move(new_web_state));
   original_url_ = url;
   FetchFavicon(url);
 
   DistillerPageIOS::DistillPageImpl(url, script);
+
+  // WKWebView sets the document.hidden property to true and the
+  // document.visibilityState to prerender if the page is not added to a view
+  // hierarchy. Some pages may not render their content in these conditions.
+  // Add the view and move it out of the screen far in the top left corner of
+  // the coordinate space.
+  CGRect frame = [[[UIApplication sharedApplication] keyWindow] frame];
+  frame.origin.x = -5 * std::max(frame.size.width, frame.size.height);
+  frame.origin.y = frame.origin.x;
+  DCHECK(![CurrentWebState()->GetView() superview]);
+  [CurrentWebState()->GetView() setFrame:frame];
+  [[[UIApplication sharedApplication] keyWindow]
+      insertSubview:CurrentWebState()->GetView()
+            atIndex:0];
 }
 
 void ReadingListDistillerPage::FetchFavicon(const GURL& page_url) {
   if (!CurrentWebState() || !page_url.is_valid()) {
     return;
   }
   favicon::WebFaviconDriver* favicon_driver =
       favicon::WebFaviconDriver::FromWebState(CurrentWebState());
   DCHECK(favicon_driver);
   favicon_driver->FetchFavicon(page_url);
 }
 
 void ReadingListDistillerPage::OnDistillationDone(const GURL& page_url,
                                                   const base::Value* value) {
   std::unique_ptr<web::WebState> old_web_state = DetachWebState();
   if (old_web_state) {
+    [old_web_state->GetView() removeFromSuperview];
     web_state_dispatcher_->ReturnWebState(std::move(old_web_state));
   }
   DistillerPageIOS::OnDistillationDone(page_url, value);
 }
 
 bool ReadingListDistillerPage::IsLoadingSuccess(
     web::PageLoadCompletionStatus load_completion_status) {
   if (load_completion_status != web::PageLoadCompletionStatus::SUCCESS) {
     return false;
   }
@@ skipping 126 matching lines @@
   if (!new_gurl.is_valid()) {
     return false;
   }
   FetchFavicon(new_gurl);
   web::NavigationManager::WebLoadParams params(new_gurl);
   CurrentWebState()->GetNavigationManager()->LoadURLWithParams(params);
   return true;
 }
 
 }  // namespace reading_list