refactor: replace --offscreen flag with ApplyWebPreferences (#28938)

patches/chromium/.patches

@@ -103,6 +103,6 @@ web_contents.patch
 fix_route_mouse_event_navigations_through_the_web_contents_delegate.patch
 disable_unload_metrics.patch
 fix_add_check_for_sandbox_then_result.patch
-moves_background_color_setter_of_webview_to_blinks_webprefs_logic.patch
+extend_apply_webpreferences.patch
 fix_expose_decrementcapturercount_in_web_contents_impl.patch
 add_setter_for_browsermainloop_result_code.patch

patches/chromium/extend_apply_webpreferences.patch

@@ -1,7 +1,7 @@
 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
 From: Samuel Attard <sattard@slack-corp.com>
 Date: Mon, 8 Mar 2021 16:27:39 -0800
-Subject: moves background_color setter of WebView to blinks webprefs logic
+Subject: extend ApplyWebPreferences with Electron-specific logic
 
 background_color can be updated at runtime, as such we need to apply the
 new background color to the WebView in the ApplyPreferences method.
@@ -12,7 +12,7 @@ Ideally we could add an embedder observer pattern here but that can be
 done in future work.
 
 diff --git a/third_party/blink/renderer/core/exported/web_view_impl.cc b/third_party/blink/renderer/core/exported/web_view_impl.cc
-index affad073f806c509779c041128708fb074fee8ad..b2615fc4ea5e9ae96182fb611a419c7c5630e983 100644
+index affad073f806c509779c041128708fb074fee8ad..0d3486f136f77375a8977cefeef1e1dea7549045 100644
 --- a/third_party/blink/renderer/core/exported/web_view_impl.cc
 +++ b/third_party/blink/renderer/core/exported/web_view_impl.cc
 @@ -155,6 +155,7 @@
@@ -23,7 +23,7 @@ index affad073f806c509779c041128708fb074fee8ad..b2615fc4ea5e9ae96182fb611a419c7c
  #include "third_party/blink/renderer/platform/graphics/image.h"
  #include "third_party/blink/renderer/platform/graphics/paint/cull_rect.h"
  #include "third_party/blink/renderer/platform/graphics/paint/paint_record_builder.h"
-@@ -1755,6 +1756,14 @@ void WebView::ApplyWebPreferences(const web_pref::WebPreferences& prefs,
+@@ -1755,6 +1756,16 @@ void WebView::ApplyWebPreferences(const web_pref::WebPreferences& prefs,
  
    RuntimeEnabledFeatures::SetTranslateServiceEnabled(
        prefs.translate_service_available);
@@ -35,6 +35,8 @@ index affad073f806c509779c041128708fb074fee8ad..b2615fc4ea5e9ae96182fb611a419c7c
 +      color = static_cast<SkColor>(blink_color);
 +  }
 +  web_view->SetBaseBackgroundColor(color);
++
++  SetUseExternalPopupMenus(!prefs.offscreen);
  }
  
  void WebViewImpl::ThemeChanged() {

shell/browser/web_contents_preferences.cc

@@ -325,13 +325,6 @@ void WebContentsPreferences::AppendCommandLineSwitches(
     }
   }
 
-  // --offscreen
-  // TODO(loc): Offscreen is duplicated in WebPreferences because it's needed
-  // earlier than we can get WebPreferences at the moment.
-  if (IsEnabled(options::kOffscreen)) {
-    command_line->AppendSwitch(options::kOffscreen);
-  }
-
 #if defined(OS_MAC)
   // Enable scroll bounce.
   if (IsEnabled(options::kScrollBounce))

shell/renderer/renderer_client_base.cc

@@ -148,17 +148,6 @@ void RendererClientBase::BindProcess(v8::Isolate* isolate,
 void RendererClientBase::RenderThreadStarted() {
   auto* command_line = base::CommandLine::ForCurrentProcess();
 
-#if BUILDFLAG(USE_EXTERNAL_POPUP_MENU)
-  // On macOS, popup menus are rendered by the main process by default.
-  // This causes problems in OSR, since when the popup is rendered separately,
-  // it won't be captured in the rendered image.
-  // TODO(loc): This will be wrong for in-process child windows, as this
-  // function won't run again for them.
-  if (command_line->HasSwitch(options::kOffscreen)) {
-    blink::WebView::SetUseExternalPopupMenus(false);
-  }
-#endif
-
 #if BUILDFLAG(ENABLE_ELECTRON_EXTENSIONS)
   auto* thread = content::RenderThread::Get();