Avoid <picture> preloading when viewport not initialized.

third_party/WebKit/Source/core/html/parser/HTMLPreloadScanner.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009 Torch Mobile, Inc. http://www.torchmobile.com/
  * Copyright (C) 2010 Google Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
@@ skipping 789 matching lines @@
       }
 
       if (match(tagImpl, pictureTag)) {
         m_inPicture = true;
         m_pictureData = PictureData();
         return;
       }
 
       StartTagScanner scanner(tagImpl, m_mediaValues);
       scanner.processAttributes(token.attributes());
-      if (m_inPicture)
+      // TODO(yoav): ViewportWidth is currently racy and might be zero in some
+      // cases, at least in tests. That problem will go away once
+      // ParseHTMLOnMainThread lands and MediaValuesCached is eliminated.
+      if (m_inPicture && m_mediaValues->viewportWidth())
         scanner.handlePictureSourceURL(m_pictureData);
       std::unique_ptr<PreloadRequest> request = scanner.createPreloadRequest(
           m_predictedBaseElementURL, source, m_clientHintsPreferences,
           m_pictureData, m_documentParameters->referrerPolicy);
       if (request)
         requests.append(std::move(request));
       return;
     }
     default: { return; }
   }
@@ skipping 68 matching lines @@
   defaultViewportMinWidth = document->viewportDefaultMinWidth();
   viewportMetaZeroValuesQuirk =
       document->settings() &&
       document->settings()->viewportMetaZeroValuesQuirk();
   viewportMetaEnabled =
       document->settings() && document->settings()->viewportMetaEnabled();
   referrerPolicy = document->getReferrerPolicy();
 }
 
 }  // namespace blink