Making sure we don't take a GestureNav screenshot unless the history position changes.

content/browser/frame_host/navigator_impl.cc

 // Copyright 2013 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/frame_host/navigator_impl.h"
 
 #include "base/command_line.h"
 #include "content/browser/frame_host/frame_tree.h"
 #include "content/browser/frame_host/frame_tree_node.h"
 #include "content/browser/frame_host/navigation_controller_impl.h"
@@ skipping 408 matching lines @@
   }
 
   if (PageTransitionIsMainFrame(params.transition)) {
     if (delegate_) {
       // When overscroll navigation gesture is enabled, a screenshot of the page
       // in its current state is taken so that it can be used during the
       // nav-gesture. It is necessary to take the screenshot here, before
       // calling RenderFrameHostManager::DidNavigateMainFrame, because that can
       // change WebContents::GetRenderViewHost to return the new host, instead
       // of the one that may have just been swapped out.
-      if (delegate_->CanOverscrollContent())
+      NavigationEntry* current_entry = controller_->GetLastCommittedEntry();
+      int32 current_page_id = current_entry ? current_entry->GetPageID() : -1;

[nasko, 2014/06/04 18:53:48]

nit: it will be a bit more readable with an empty line following.

[mfomitchev, 2014/06/04 19:26:20]

Done.

+      // If page id didn't change, then this is not a navigation to a new
+      // history entry or to the previous entry, and we don't need to take the
+      // screenshot.

[nasko, 2014/06/04 18:53:48]

nit: For back/forward navigations we still want to take screenshots, so what
this is trying to single out is exactly the case where the same history entry is
used. The comment as is implies that only going back to the previous history
entry or new navigations are of interest.

[mfomitchev, 2014/06/04 19:26:20]

Reworded

+      bool page_id_changed = params.page_id > 0 &&
+          params.page_id != current_page_id;
+      if (delegate_->CanOverscrollContent() && page_id_changed)
         controller_->TakeScreenshot();
 
       // Run tasks that must execute just before the commit.
       delegate_->DidNavigateMainFramePreCommit(params);
     }
 
     if (!use_site_per_process)
       frame_tree->root()->render_manager()->DidNavigateFrame(render_frame_host);
   }
 
@@ skipping 174 matching lines @@
 
     // Navigations in Web UI pages count as browser-initiated navigations.
     params.is_renderer_initiated = false;
   }
 
   if (delegate_)
     delegate_->RequestOpenURL(render_frame_host, params);
 }
 
 }  // namespace content