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

content/browser/tab_contents/tab_contents.cc

 // Copyright (c) 2011 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.
 
 #include "content/browser/tab_contents/tab_contents.h"
 
 #include <cmath>
 
 #include "base/command_line.h"
 #include "base/metrics/histogram.h"
@@ skipping 1783 matching lines @@
   upload_position_ = upload_position;
   upload_size_ = upload_size;
   load_state_host_ = net::IDNToUnicode(url.host(),
       content::GetContentClient()->browser()->GetAcceptLangs(this));
   if (load_state_ == net::LOAD_STATE_READING_RESPONSE)
     SetNotWaitingForResponse();
   if (IsLoading())
     NotifyNavigationStateChanged(INVALIDATE_LOAD | INVALIDATE_TAB);
 }
 
+void TabContents::OffsetAndPruneHistory(int offset) {
+  // TODO(cbentzel): Should this pass in a SiteInstance and a page_id to
+  // make sure we get the right one.

[gavinp, 2011/08/08 16:39:47]

NIT: Use a question mark on questions.

+  RenderViewHost* rvh = render_view_host();
+  if (!rvh)
+    return;
+  rvh->Send(new ViewMsg_OffsetAndPruneHistory(rvh->routing_id(), offset));
+}
+
 void TabContents::WorkerCrashed() {
   if (delegate())
     delegate()->WorkerCrashed(this);
 }
 
 void TabContents::BeforeUnloadFiredFromRenderManager(
     bool proceed,
     bool* proceed_to_fire_unload) {
   if (delegate())
     delegate()->BeforeUnloadFired(this, proceed, proceed_to_fire_unload);
@@ skipping 90 matching lines @@
 }
 
 void TabContents::SwapInRenderViewHost(RenderViewHost* rvh) {
   render_manager_.SwapInRenderViewHost(rvh);
 }
 
 void TabContents::CreateViewAndSetSizeForRVH(RenderViewHost* rvh) {
   RenderWidgetHostView* rwh_view = view()->CreateViewForWidget(rvh);
   rwh_view->SetSize(view()->GetContainerSize());
 }