Teach navigation throttles how to cancel requests in WillProcessResponse.

content/public/browser/navigation_throttle.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_NAVIGATION_THROTTLE_H_
 #define CONTENT_PUBLIC_BROWSER_NAVIGATION_THROTTLE_H_
 
 #include "content/common/content_export.h"
 
 namespace content {
@@ skipping 37 matching lines @@
 
   // Called when a server redirect is received by the navigation.
   //
   // The implementer is responsible for ensuring that the WebContents this
   // throttle is associated with remain alive during the duration of this
   // method. Failing to do so will result in use-after-free bugs. Should the
   // implementer need to destroy the WebContents, it should return CANCEL,
   // CANCEL_AND_IGNORE or DEFER and perform the destruction asynchronously.
   virtual ThrottleCheckResult WillRedirectRequest();
 
+  // Called when a response's headers and metadata are available.
+  //
+  // The implementer is responsible for ensuring that the WebContents this
+  // throttle is associated with remain alive during the duration of this
+  // method. Failing to do so will result in use-after-free bugs. Should the
+  // implementer need to destroy the WebContents, it should return CANCEL,
+  // CANCEL_AND_IGNORE and perform the destruction asynchronously. The

[clamy, 2016/01/25 16:36:21]

Let's remove last condition. There is one known case of a Throttle that will
need to use it (SafeBrowsing on Android).

Also content/public question here for nasko: we're not supposed to land
something in the public API if it's not used outside of content. However,
there's no impl version of the NavigationThrottle, since it's an interface
that's meant to be implemented outside of content. How do we deal with that
case?

[Mike West, 2016/01/26 09:41:42]

Done.

+  // implementer MUST NOT return DEFER.
+  virtual ThrottleCheckResult WillProcessResponse();
+
   // The NavigationHandle that is tracking the information related to this
   // navigation.
   NavigationHandle* navigation_handle() const { return navigation_handle_; }
 
  private:
   NavigationHandle* navigation_handle_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_NAVIGATION_THROTTLE_H_