Implement NavigationThrottle::BLOCK_REQUEST_AND_COLLAPSE.

content/public/browser/navigation_throttle.h

Index: content/public/browser/navigation_throttle.h
diff --git a/content/public/browser/navigation_throttle.h b/content/public/browser/navigation_throttle.h
index eb079fa40f64618dea62f18e6cb89bbab9573f7a..f505c86783a82e377d1642170dedd2e466530c07 100644
--- a/content/public/browser/navigation_throttle.h
+++ b/content/public/browser/navigation_throttle.h
@@ -40,6 +40,12 @@ class CONTENT_EXPORT NavigationThrottle {
     // is navigated.
     BLOCK_REQUEST,
 
+    // Blocks a navigation taking place in a subframe, and collapses the frame
+    // owner element in the parent document (i.e. removes it from the layout).
+    // This can only be returned from WillStartRequest, and also from
+    // WillRedirectRequest when PlzNavigate is enabled.
+    BLOCK_REQUEST_AND_COLLAPSE,
+
     // Blocks a navigation due to rules asserted by a response (for instance,
     // embedding restrictions like 'X-Frame-Options'). This result will only
     // be returned from WillProcessResponse.