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);
+
+    const bool isSlowConnection = networkStateNotifier().connectionType() == WebConnectionTypeCellular2G;
+    const bool disallowFetch = document.settings()->disallowFetchForDocWrittenScriptsInMainFrame() || (document.settings()->disallowFetchForDocWrittenScriptsInMainFrameOnSlowConnections() && isSlowConnection);
+    if (!disallowFetch)

[Bryan McQuade, 2016/05/03 20:22:48]

this could be updated to just
return disallowFetch;

+        return false;
+
     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