Implement NavigationThrottle::BLOCK_REQUEST_AND_COLLAPSE.

content/common/frame_messages.h

 // Copyright 2013 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.
 
 // IPC messages for interacting with frames.
 // Multiply-included message file, hence no include guard.
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 739 matching lines @@
 // renderer.
 IPC_MESSAGE_ROUTED1(FrameMsg_FocusedFormFieldDataRequest, int /* request_id */)
 
 // Change the accessibility mode in the renderer process.
 IPC_MESSAGE_ROUTED1(FrameMsg_SetAccessibilityMode,
                     AccessibilityMode)
 
 // Dispatch a load event in the iframe element containing this frame.
 IPC_MESSAGE_ROUTED0(FrameMsg_DispatchLoad)
 
+// Sent to a subframe to control whether to collapse its the frame owner element
+// in the embedder document, that is, to remove it from the layout as if it did
+// not exist.
+IPC_MESSAGE_ROUTED1(FrameMsg_Collapse, bool /* collapsed */)
+
 // Notifies the frame that its parent has changed the frame's sandbox flags.
 IPC_MESSAGE_ROUTED1(FrameMsg_DidUpdateSandboxFlags, blink::WebSandboxFlags)
 
 // Update a proxy's window.name property.  Used when the frame's name is
 // changed in another process.
 IPC_MESSAGE_ROUTED2(FrameMsg_DidUpdateName,
                     std::string /* name */,
                     std::string /* unique_name */)
 
 // Updates replicated ContentSecurityPolicy in a frame proxy.
@@ skipping 820 matching lines @@
 // nearest find result in the sending frame.
 IPC_MESSAGE_ROUTED2(FrameHostMsg_GetNearestFindResult_Reply,
                     int /* nfr_request_id */,
                     float /* distance */)
 #endif
 
 // Adding a new message? Stick to the sort order above: first platform
 // independent FrameMsg, then ifdefs for platform specific FrameMsg, then
 // platform independent FrameHostMsg, then ifdefs for platform specific
 // FrameHostMsg.