Discard compositor frames from unloaded web content

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 286 matching lines @@
 
   // True if the document for the load is a unique origin that should be
   // considered potentially trustworthy.
   IPC_STRUCT_MEMBER(bool, has_potentially_trustworthy_unique_origin)
 
   // See WebSearchableFormData for a description of these.
   // Not used by PlzNavigate: in that case these fields are sent to the browser
   // in BeginNavigationParams.
   IPC_STRUCT_MEMBER(GURL, searchable_form_url)
   IPC_STRUCT_MEMBER(std::string, searchable_form_encoding)
+
+  // This is a non-decreasing value that the browser process can use to
+  // identify and discard compositor frames that correspond to now-unloaded
+  // web content.
+  IPC_STRUCT_MEMBER(uint32_t, content_source_id)
 IPC_STRUCT_END()
 
 IPC_STRUCT_BEGIN(FrameMsg_PostMessage_Params)
   // Whether the data format is supplied as serialized script value, or as
   // a simple string. If it is a raw string, must be converted from string to a
   // WebSerializedScriptValue in the renderer process.
   IPC_STRUCT_MEMBER(bool, is_data_raw_string)
 
   // The serialized script value.
   IPC_STRUCT_MEMBER(base::string16, data)
@@ skipping 1294 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.