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

content/browser/tab_contents/navigation_controller.cc

Index: content/browser/tab_contents/navigation_controller.cc
diff --git a/content/browser/tab_contents/navigation_controller.cc b/content/browser/tab_contents/navigation_controller.cc
index e29ecc31ded29d91e7b56219710a56d94a821cfe..b9dd8dab0b1694c5ad2d3dd34535f43361a44f27 100644
--- a/content/browser/tab_contents/navigation_controller.cc
+++ b/content/browser/tab_contents/navigation_controller.cc
@@ -342,6 +342,11 @@ void NavigationController::GoBack() {
   // Base the navigation on where we are now...
   int current_index = GetCurrentEntryIndex();
 
+  LOG(ERROR) << "GoBack";
+  for (int i = 0; i < current_index; ++i) {
+    LOG(ERROR) << entries_[i]->url().spec();
+  }
+
   DiscardNonCommittedEntries();
 
   pending_entry_index_ = current_index - 1;
@@ -616,7 +621,7 @@ NavigationType::Type NavigationController::ClassifyNavigation(
     // The page was not found. It could have been pruned because of the limit on
     // back/forward entries (not likely since we'll usually tell it to navigate
     // to such entries). It could also mean that the renderer is smoking crack.
-    NOTREACHED();
+    //NOTREACHED();
 
     // Because the unknown entry has committed, we risk showing the wrong URL in
     // release builds. Instead, we'll kill the renderer process to be safe.
@@ -676,9 +681,12 @@ bool NavigationController::IsRedirect(
 
 void NavigationController::RendererDidNavigateToNewPage(
     const ViewHostMsg_FrameNavigate_Params& params, bool* did_replace_entry) {
+  LOG(ERROR) << "RendererDidNavigateToNewPage."
+             << " url=" << params.url;
   NavigationEntry* new_entry;
   bool update_virtual_url;
   if (pending_entry_) {
+    LOG(ERROR) << "Pending Entry exists";
     // TODO(brettw) this assumes that the pending entry is appropriate for the
     // new page that was just loaded. I don't think this is necessarily the
     // case! We should have some more tracking to know for sure.
@@ -712,6 +720,8 @@ void NavigationController::RendererDidNavigateToNewPage(
 
 void NavigationController::RendererDidNavigateToExistingPage(
     const ViewHostMsg_FrameNavigate_Params& params) {
+  LOG(ERROR) << "RendererDidNavigateToExistingPage."
+             << " url=" << params.url;
   // We should only get here for main frame navigations.
   DCHECK(PageTransition::IsMainFrame(params.transition));
 
@@ -931,6 +941,11 @@ void NavigationController::CopyStateFromAndPrune(NavigationController* source,
     if (last_committed_entry_index_ != -1)
       last_committed_entry_index_--;
   }
+
+  LOG(ERROR) << "OffsetAndPrune."
+             << " last_committed_entry_index_=" << last_committed_entry_index_;
+  // Send a message to active render view asking to offset messages.
+  tab_contents_->OffsetAndPruneHistory(entry_count() - 1);
 }
 
 void NavigationController::PruneAllButActive() {