Fix regression with back-button not working on prerendered and instant pages.

content/renderer/render_view.cc

Index: content/renderer/render_view.cc
diff --git a/content/renderer/render_view.cc b/content/renderer/render_view.cc
index 972349f99357ff3f7c6cac7319e352f3c04c2599..6f3d7c99c578a8eff9014ce14eeabbfe90f42a6f 100644
--- a/content/renderer/render_view.cc
+++ b/content/renderer/render_view.cc
@@ -703,6 +703,8 @@ bool RenderView::OnMessageReceived(const IPC::Message& message) {
 #endif
     IPC_MESSAGE_HANDLER(ViewMsg_UpdateRemoteAccessClientFirewallTraversal,
                         OnUpdateRemoteAccessClientFirewallTraversal)
+    IPC_MESSAGE_HANDLER(ViewMsg_OffsetAndPruneHistory,
+                        OnOffsetAndPruneHistory)
     // Have the super handle all other messages.
     IPC_MESSAGE_UNHANDLED(handled = RenderWidget::OnMessageReceived(message))
   IPC_END_MESSAGE_MAP()
@@ -1017,6 +1019,22 @@ void RenderView::OnScrollFocusedEditableNodeIntoView() {
   }
 }
 
+void RenderView::OnOffsetAndPruneHistory(int offset) {
+  int current_page_id = -1;

[tburkard, 2011/08/09 17:36:03]

I'd add a comment explaining what this does (either here or in the headerfile)

[cbentzel, 2011/08/09 19:12:14]

I did this at the ViewMsg declaration, which looked more consistent.

+  if (history_list_offset_ >= 0) {

[brettw, 2011/08/09 18:14:40]

No {} for single-line conditionals.

[cbentzel, 2011/08/09 19:12:14]

Done.

+    current_page_id = history_page_ids_[history_list_offset_];
+  }
+
+  history_list_offset_ = offset;
+  history_list_length_ = offset + 1;
+  if (history_list_length_ >= 0)

[brettw, 2011/08/09 18:14:40]

What case will the history_list_length_ be negative? That seems suspicious.

[cbentzel, 2011/08/09 19:12:14]

That would be suspicious. Removed during the migration to the new version. I do
still check for negative history_list_offset_ because this may be swapped in
after a Navigate message but before a didCommitProvisionalLoad.

+    history_page_ids_.resize(history_list_length_, -1);
+  // Older entries also need to be invalidated.
+  for (int i = 0; i < history_list_offset_; ++i)

[brettw, 2011/08/09 18:14:40]

I think this version is a bit easier to follow:

// <clear comment about what type of list we're trying to generate>.
std::vector<int32> new_page_ids_;
new_page_ids.resize(history_list_length_, -1);
new_page_ids[history_list_offset_] = current_page_id;
history_page_ids.swap(new_page_ids);

[cbentzel, 2011/08/09 19:12:14]

Yes, that's cleaner. Moved to that.

+    history_page_ids_[i] = -1;
+  history_page_ids_[history_list_offset_] = current_page_id;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 // Tell the embedding application that the URL of the active page has changed