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())
-        controller_->TakeScreenshot();
+      if (delegate_->CanOverscrollContent()) {
+        bool page_id_changed;
+        bool url_changed;
+        NavigationEntry* current_entry = controller_->GetLastCommittedEntry();
+        if (current_entry) {
+          page_id_changed = params.page_id > 0 &&
+              params.page_id != current_entry->GetPageID();
+          url_changed = params.url != current_entry->GetURL();
+        } else {
+          page_id_changed = params.page_id > 0;
+          url_changed = params.url != GURL::EmptyGURL();
+        }
+
+        // We only want to take the screenshot if the are navigating to a
+        // different history entry than the current one. So if neither the
+        // page id nor the url changed - don't take the screenshot.
+        if (page_id_changed || url_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);
   }
 
   // When using --site-per-process, we notify the RFHM for all navigations,
@@ skipping 173 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