Log to UMA when x-origin frames (1) are created and (2) become visible

third_party/WebKit/Source/core/frame/Frame.cpp

Index: third_party/WebKit/Source/core/frame/Frame.cpp
diff --git a/third_party/WebKit/Source/core/frame/Frame.cpp b/third_party/WebKit/Source/core/frame/Frame.cpp
index 1c763fee1b4523a7ba75d0d6ed6732b0f6607e4f..ff3ed4d667f058cf1fdb14c8817b3427c43a447c 100644
--- a/third_party/WebKit/Source/core/frame/Frame.cpp
+++ b/third_party/WebKit/Source/core/frame/Frame.cpp
@@ -281,7 +281,9 @@ Settings* Frame::settings() const
 bool Frame::isCrossOrigin() const
 {
     // Check to see if the frame can script into the top level document.
-    const SecurityOrigin* securityOrigin = securityContext()->getSecurityOrigin();
+    SecurityContext* context = securityContext();
+    DCHECK(context);
+    const SecurityOrigin* securityOrigin = context->getSecurityOrigin();
     Frame* top = tree().top();
     return top && !securityOrigin->canAccess(top->securityContext()->getSecurityOrigin());
 }