overscroll: Enable overscroll navigation by default.

content/browser/renderer_host/render_widget_host_impl.cc

 // Copyright (c) 2012 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/renderer_host/render_widget_host_impl.h"
 
 #include <math.h>
 #include <utility>
 
 #include "base/auto_reset.h"
@@ skipping 167 matching lines @@
   }
 
   is_threaded_compositing_enabled_ = IsThreadedCompositingEnabled();
 
   process_->Attach(this, routing_id_);
   // Because the widget initializes as is_hidden_ == false,
   // tell the process host that we're alive.
   process_->WidgetRestored();
 
 #if defined(USE_AURA)
-  bool overscroll_enabled = CommandLine::ForCurrentProcess()->
-      HasSwitch(switches::kEnableOverscrollHistoryNavigation);
+  bool overscroll_enabled = !CommandLine::ForCurrentProcess()->
+      HasSwitch(switches::kDisableOverscrollHistoryNavigation);
   if (overscroll_enabled)
     InitializeOverscrollController();
 #endif
 }
 
 RenderWidgetHostImpl::~RenderWidgetHostImpl() {
   SetView(NULL);
 
   // Clear our current or cached backing store if either remains.
   BackingStoreManager::RemoveBackingStore(this);
@@ skipping 2162 matching lines @@
     return;
 
   OnRenderAutoResized(new_size);
 }
 
 void RenderWidgetHostImpl::DetachDelegate() {
   delegate_ = NULL;
 }
 
 }  // namespace content