Metrics for document.write script blocking

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

Index: third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
diff --git a/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp b/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
index f2cbded4f2adefc8f3706cb283e862b355a7fc52..f4cc514ba74c71905f196abd876dbc0570ee0171 100644
--- a/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
+++ b/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
@@ -89,29 +89,38 @@ bool shouldDisallowFetchForMainFrameScript(const ResourceRequest& request, Fetch
     if (!document.frame())
         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)
+    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;
 
-    // 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;
-
     return true;
 }