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..b5b5fd6323c268c04eb3ab5a20d50cb3bb5a4c50 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_SetHistoryLengthAndClear,
+                        OnSetHistoryLengthAndClear)
     // Have the super handle all other messages.
     IPC_MESSAGE_UNHANDLED(handled = RenderWidget::OnMessageReceived(message))
   IPC_END_MESSAGE_MAP()
@@ -1017,6 +1019,21 @@ void RenderView::OnScrollFocusedEditableNodeIntoView() {
   }
 }
 
+void RenderView::OnSetHistoryLengthAndClear(int history_length) {
+  DCHECK(history_length >= 0);
+  DCHECK(history_list_length_ == 0 || history_list_length_ == 1);

[Charlie Reis, 2011/08/09 20:59:31]

Should we return early if this isn't the case?  Release builds will proceed
without hitting this DCHECK, and it doesn't seem safe to continue if we're not
in this initial state.

[cbentzel, 2011/08/09 21:21:12]

Yes. Changed to returning early.

+  int current_page_id = -1;

[Charlie Reis, 2011/08/09 20:59:31]

I think the page_id_ field should be the same thing, right?  Maybe you can use
that and DCHECK that it's correct.

+  if (history_list_offset_ >= 0)
+    current_page_id = history_page_ids_[history_list_offset_];
+  int new_history_list_length = history_length + history_list_length_;

[Charlie Reis, 2011/08/09 20:59:31]

Why are we adding the two?  It sounds like we're supposed to be setting it to
the given history_length, but this shifts it by the given amount.

More specifically, are there actually separate cases when the
history_list_length_ will be 0 and 1?  I would have guessed it to be 1, and just
set the history_list_length_ to the argument plus 1.

[cbentzel, 2011/08/09 21:21:12]

The prerendered page could be swapped in between the initial navigate and the
commit of the provisional load, when history_list_length_ is 0. I added a
comment for this.

+  std::vector<int32> new_history_page_ids_(new_history_list_length, -1);
+  if (current_page_id != -1)
+    new_history_page_ids_[new_history_list_length - 1] = current_page_id;
+  new_history_page_ids_.swap(history_page_ids_);
+  history_list_offset_ = new_history_list_length - 1;
+  history_list_length_ = new_history_list_length;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 // Tell the embedding application that the URL of the active page has changed