Metrics for document.write script blocking

third_party/WebKit/Source/core/loader/FrameFetchContext.cpp

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 71 matching lines @@
     // fetch disallowed.
     if (!document.isInDocumentWrite())
         return false;
 
     if (!document.settings())
         return false;
 
     if (!document.frame())
         return false;
 
-    // Do not block scripts if it is a page reload. This is to enable pages to
-    // recover if blocking of a script is leading to a page break and the user
-    // reloads the page.
-    const FrameLoadType loadType = document.frame()->loader().loadType();
-    const bool isReload = (loadType == FrameLoadTypeReload || loadType == FrameLoadTypeReloadBypassingCache || loadType == FrameLoadTypeSame);
-    if (isReload)
-        return false;
-
     const bool isSlowConnection = networkStateNotifier().connectionType() == WebConnectionTypeCellular2G;
     const bool disallowFetch = document.settings()->disallowFetchForDocWrittenScriptsInMainFrame() || (document.settings()->disallowFetchForDocWrittenScriptsInMainFrameOnSlowConnections() && isSlowConnection);
     if (!disallowFetch)
         return false;
 
     // Only block synchronously loaded (parser blocking) scripts.
     if (defer != FetchRequest::NoDefer)
         return false;
 
     // Avoid blocking same origin scripts, as they may be used to render main
     // page content, whereas cross-origin scripts inserted via document.write
     // are likely to be third party content.
     if (request.url().host() == document.getSecurityOrigin()->domain())
         return false;
 
+    // Do not block scripts if it is a page reload. This is to enable pages to
+    // recover if blocking of a script is leading to a page break and the user
+    // reloads the page.
+    const FrameLoadType loadType = document.frame()->loader().loadType();
+    const bool isReload = loadType == FrameLoadTypeReload || loadType == FrameLoadTypeReloadBypassingCache || loadType == FrameLoadTypeSame;
+    if (isReload) {
+        // Recording this metric since an increase in number of reloads for pages
+        // where a script was blocked could be indicative of a page break.
+        document.loader()->didObserveLoadingBehavior(WebLoadingBehaviorFlag::WebLoadingBehaviorDocumentWriteBlockReload);
+        return false;
+    }
+
+    // Add the metadata that this page has scripts inserted via document.write
+    // that are eligible for blocking. Note that if there are multiple scripts
+    // the flag will be conveyed to the browser process only once.
+    document.loader()->didObserveLoadingBehavior(WebLoadingBehaviorFlag::WebLoadingBehaviorDocumentWriteBlock);

[Bryan McQuade, 2016/04/30 01:10:09]

i notice this will only trigger if the setting is enabled, which means we won't
get any hits in our control population. is that intended? do we instead want to
observe loading behavior  as long as we would have blocked the script load,
regardless of whether the setting is enabled? similar question for the reload
case.

[shivanisha, 2016/04/30 19:11:11]

Thanks for the catch. I will upload the fixed version and also check if I can
add a browser test to test this.

     return true;
 }
 
 } // namespace
 
 FrameFetchContext::FrameFetchContext(DocumentLoader* loader, Document* document)
     : m_document(document)
     , m_documentLoader(loader)
     , m_imageFetched(false)
 {
@@ skipping 679 matching lines @@
 }
 
 DEFINE_TRACE(FrameFetchContext)
 {
     visitor->trace(m_document);
     visitor->trace(m_documentLoader);
     FetchContext::trace(visitor);
 }
 
 } // namespace blink