Don't fire onbeforeunload for same document history navigations with PlzNavigate.

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 <utility>
 
 #include "base/logging.h"
 #include "base/metrics/histogram_macros.h"
@@ skipping 1109 matching lines @@
                                       LoFiState lofi_state,
                                       bool is_same_document_history_load,
                                       bool is_history_navigation_in_new_child,
                                       base::TimeTicks navigation_start) {
   CHECK(IsBrowserSideNavigationEnabled());
   DCHECK(frame_tree_node);
 
   // This value must be set here because creating a NavigationRequest might
   // change the renderer live/non-live status and change this result.
   bool should_dispatch_beforeunload =
+      !is_same_document_history_load &&
       frame_tree_node->current_frame_host()->ShouldDispatchBeforeUnload();
   FrameMsg_Navigate_Type::Value navigation_type =
       GetNavigationType(controller_->GetBrowserContext(), entry, reload_type);
   std::unique_ptr<NavigationRequest> scoped_request =
       NavigationRequest::CreateBrowserInitiated(
           frame_tree_node, dest_url, dest_referrer, frame_entry, entry,
           navigation_type, lofi_state, is_same_document_history_load,
           is_history_navigation_in_new_child, navigation_start, controller_);
   NavigationRequest* navigation_request = scoped_request.get();
 
@@ skipping 121 matching lines @@
     if (navigation_handle)
       navigation_handle->update_entry_id_for_transfer(entry->GetUniqueID());
 
     controller_->SetPendingEntry(std::move(entry));
     if (delegate_)
       delegate_->NotifyChangedNavigationState(content::INVALIDATE_TYPE_URL);
   }
 }
 
 }  // namespace content