Add a way to cancel deferred navigations in NavigationHandle

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 c5202ae71d89d47990394423a87c943af488d66c..2156948004330068cd459822a06d5e10f90fd809 100644
--- a/content/public/browser/navigation_throttle.h
+++ b/content/public/browser/navigation_throttle.h
@@ -17,8 +17,18 @@ class CONTENT_EXPORT NavigationThrottle {
   // This is returned to the NavigationHandle to allow the navigation to
   // proceed, or to cancel it.
   enum ThrottleCheckResult {
+    // The navigation proceeds uninterrupted.
     PROCEED,
+
+    // Defers the navigation until the NavigationThrottle calls
+    // NavigationHandle::Resume or NavigationHandle::CancelDeferredRequest.
     DEFER,
+
+    // Cancels the navigation.
+    CANCEL,
+
+    // Cancels the navigation and makes the requester of the navigation acts
+    // like the request was never made.
     CANCEL_AND_IGNORE,
   };