Dev tools warning and console warning 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 c08ee5f31a0503f3eaff2cf213ad4023c961e87e..944bb610135809a4bbcbe7a32d8d415df9ef0907 100644
--- a/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
+++ b/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
@@ -78,6 +78,13 @@ namespace blink {
 
 namespace {
 
+void emitWarningForDocWriteScripts(const String& url, const Document& document)
+{
+    String message = "A Parser-blocking, cross-origin script " + url + " is invoked via document.write. This may get blocked by the browser in slow connections. It is recommended to invoke this script asynchronously.";

[jkarlin, 2016/06/10 18:38:36]

There should also be a link to a help page explaining (a little bit) how to make
code asynchronous. That can likely wait until after field trials however. Please
create a new bug to add the link so that we don't forget.

[jkarlin, 2016/06/10 18:38:36]

Commas needed around the url.

s/may get blocked/may be blocked/

s/in slow connections/if the device has poor network connectivity/

"recommended to invoke" doesn't make sense.

[shivanisha, 2016/06/20 14:28:06]

Created https://bugs.chromium.org/p/chromium/issues/detail?id=621520

Updated the warning string. Removed the "recommended to invoke" part as that
would be replaced by the help link.

+    const_cast <Document &>(document).addConsoleMessage(ConsoleMessage::create(JSMessageSource, WarningMessageLevel, message));

[Nate Chapin, 2016/06/10 23:34:32]

Nit: Pass the Document non-const instead of const_cast'ing.

[shivanisha, 2016/06/20 14:28:06]

done.

+    WTFLogAlways("%s", message.utf8().data());
+}
+
 bool shouldDisallowFetchForMainFrameScript(const ResourceRequest& request, FetchRequest::DeferOption defer, const Document& document)
 {
     // Only scripts inserted via document.write are candidates for having their
@@ -113,6 +120,7 @@ bool shouldDisallowFetchForMainFrameScript(const ResourceRequest& request, Fetch
         // 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);
+        emitWarningForDocWriteScripts(request.url().getString(), document);
         return false;
     }
 
@@ -121,6 +129,8 @@ bool shouldDisallowFetchForMainFrameScript(const ResourceRequest& request, Fetch
     // the flag will be conveyed to the browser process only once.
     document.loader()->didObserveLoadingBehavior(WebLoadingBehaviorFlag::WebLoadingBehaviorDocumentWriteBlock);
 
+    emitWarningForDocWriteScripts(request.url().getString(), document);
+
     const bool isSlowConnection = networkStateNotifier().connectionType() == WebConnectionTypeCellular2G;
     const bool disallowFetch = document.settings()->disallowFetchForDocWrittenScriptsInMainFrame() || (document.settings()->disallowFetchForDocWrittenScriptsInMainFrameOnSlowConnections() && isSlowConnection);