Blocking synchronous and third party doc.written scripts

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 f040553594f41cd97ae0e4d1ae27be96348e4b53..4923f218eccb92c32d0395a2b39512febfb7addb 100644
--- a/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
+++ b/third_party/WebKit/Source/core/loader/FrameFetchContext.cpp
@@ -56,6 +56,7 @@
 #include "core/loader/PingLoader.h"
 #include "core/loader/ProgressTracker.h"
 #include "core/loader/appcache/ApplicationCacheHost.h"
+#include "core/page/NetworkStateNotifier.h"
 #include "core/page/Page.h"
 #include "core/svg/graphics/SVGImageChromeClient.h"
 #include "core/timing/DOMWindowPerformance.h"
@@ -173,7 +174,7 @@ static ResourceRequestCachePolicy memoryCachePolicyToResourceRequestCachePolicy(
     return UseProtocolCachePolicy;
 }
 
-ResourceRequestCachePolicy FrameFetchContext::resourceRequestCachePolicy(const ResourceRequest& request, Resource::Type type) const
+ResourceRequestCachePolicy FrameFetchContext::resourceRequestCachePolicy(const ResourceRequest& request, Resource::Type type, FetchRequest::DeferOption defer) const
 {
     ASSERT(frame());
     if (type == Resource::MainResource) {
@@ -208,10 +209,15 @@ ResourceRequestCachePolicy FrameFetchContext::resourceRequestCachePolicy(const R
     // future, we'll extend this logic to only block if estimated network RTT
     // is above some threshold.
     if (type == Resource::Script && isMainFrame()) {
-        const bool isInDocumentWrite = m_document && m_document->isInDocumentWrite();
         const bool disallowFetchForDocWriteScripts = frame()->settings() && frame()->settings()->disallowFetchForDocWrittenScriptsInMainFrame();
-        if (isInDocumentWrite && disallowFetchForDocWriteScripts)
-            return ReturnCacheDataDontLoad;
+        const bool isInDocumentWrite = m_document && m_document->isInDocumentWrite();
+        if (isInDocumentWrite && disallowFetchForDocWriteScripts) {
+            const bool isSync = (defer == FetchRequest::NoDefer);
+            const bool isThirdParty = (request.url().host() != m_document->getSecurityOrigin()->domain());

[Bryan McQuade, 2016/04/05 12:46:11]

let's add a comment here noting that we continue to allow same origin scripts to
run because they may be used to render main page content, whereas we block
cross-origin scripts because they are likely for third party content.

i just want to make sure readers of the code understand that we aren't doing an
origin check for security reasons (might be worth noting that in the comment
too) which is the more common reason to compare origins.

+            const bool isSlowConnection = networkStateNotifier().connectionType() == WebConnectionTypeCellular2G;

[Bryan McQuade, 2016/04/05 12:46:11]

Let's add a comment that for now we restrict slow connections to 2G, but that we
might try to expand coverage using the network quality estimator in the future.

+            if (isSync && isThirdParty && isSlowConnection)
+                return ReturnCacheDataDontLoad;
+        }
     }
 
     if (request.isConditional())