Fix user agent overridding with PlzNavigate.

content/browser/frame_host/interstitial_page_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/interstitial_page_impl.h"
 
 #include <utility>
 #include <vector>
 
 #include "base/bind.h"
@@ skipping 513 matching lines @@
     // Hide the original RVH since we're showing the interstitial instead.
     rwh_view->Hide();
   }
 }
 
 WebContents* InterstitialPageImpl::OpenURL(const OpenURLParams& params) {
   NOTREACHED();
   return nullptr;
 }
 
+const std::string& InterstitialPageImpl::GetUserAgentOverride() const {
+  return base::EmptyString();
+}
+
 RendererPreferences InterstitialPageImpl::GetRendererPrefs(
     BrowserContext* browser_context) const {
   delegate_->OverrideRendererPrefs(&renderer_preferences_);
   return renderer_preferences_;
 }
 
 void InterstitialPageImpl::RenderWidgetDeleted(
     RenderWidgetHostImpl* render_widget_host) {
   // TODO(creis): Remove this method once we verify the shutdown path is sane.
   CHECK(!web_contents_);
@@ skipping 423 matching lines @@
 void InterstitialPageImpl::UpdateDeviceScaleFactor(double device_scale_factor) {
   WebContentsImpl* web_contents_impl =
       static_cast<WebContentsImpl*>(web_contents_);
   if (!web_contents_impl)
     return;
 
   web_contents_impl->UpdateDeviceScaleFactor(device_scale_factor);
 }
 
 }  // namespace content