Update viewport_meta setting on any navigation.

content/browser/frame_host/navigation_controller_impl.cc

Index: content/browser/frame_host/navigation_controller_impl.cc
diff --git a/content/browser/frame_host/navigation_controller_impl.cc b/content/browser/frame_host/navigation_controller_impl.cc
index 5bde4bb4340d76cb67cc37f410824c5a814269d9..5a3d24baaff0ead84ee2c90604c797c5fa0a673c 100644
--- a/content/browser/frame_host/navigation_controller_impl.cc
+++ b/content/browser/frame_host/navigation_controller_impl.cc
@@ -1219,6 +1219,12 @@ void NavigationControllerImpl::RendererDidNavigateToExistingPage(
     // SSLStatus.
     if (!is_in_page)
       entry->GetSSL() = handle->ssl_status();
+
+    // Back/forward navigations can alter "request desktop site" state.
+    if (entry && GetLastCommittedEntry() &&
+        entry->GetIsOverridingUserAgent() !=
+            GetLastCommittedEntry()->GetIsOverridingUserAgent())
+      delegate_->UpdateOverridingUserAgent();
   } else {
     // This is renderer-initiated. The only kinds of renderer-initated
     // navigations that are EXISTING_PAGE are reloads and location.replace,