Send a subtree of same-process PageStates for back/forward child frames.

content/renderer/render_view_impl.h

 // Copyright (c) 2012 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_RENDERER_RENDER_VIEW_IMPL_H_
 #define CONTENT_RENDERER_RENDER_VIEW_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 699 matching lines @@
   // navigations, the history may have some entries that were committed in other
   // processes.  We won't know about them until the next navigation in this
   // process.
   int history_list_length_;
 
   // Counter to track how many frames have sent start notifications but not stop
   // notifications. TODO(avi): Remove this once DidStartLoading/DidStopLoading
   // are gone.
   int frames_in_progress_;
 
+  // Keeps track of the unique names of future subframes that the browser
+  // process has history items for during a history navigation, as well as the
+  // corresponding PageState to use when creating such frames during a
+  // back/forward navigation.  This map includes state for any frames in the
+  // page, even when concurrent back/forward navigations affect different
+  // subtrees.
+  //
+  // If the PageState for a frame is empty, the history item needs to load in a
+  // different process, so the renderer process should ask the browser process
+  // to handle it instead
+  //
+  // This state is incrementally cleared as it is used.
+  // TODO(creis): Can it be reset at any point?  This seems important, so that a
+  // frame on one page doesn't use an unused history item from the previous
+  // page.
+  std::unordered_map<std::string, PageState> history_page_states_;
+
   // UI state ------------------------------------------------------------------
 
   // The state of our target_url transmissions. When we receive a request to
   // send a URL to the browser, we set this to TARGET_INFLIGHT until an ACK
   // comes back - if a new request comes in before the ACK, we store the new
   // URL in pending_target_url_ and set the status to TARGET_PENDING. If an
   // ACK comes back and we are in TARGET_PENDING, we send the stored URL and
   // revert to TARGET_INFLIGHT.
   //
   // We don't need a queue of URLs to send, as only the latest is useful.
@@ skipping 122 matching lines @@
   // use the Observer interface to filter IPC messages and receive frame change
   // notifications.
   // ---------------------------------------------------------------------------
 
   DISALLOW_COPY_AND_ASSIGN(RenderViewImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_VIEW_IMPL_H_