refactor: turn OnOffscreen message into a command-line flag (#17687)

This turns the AtomViewMsg_Offscreen message, which only called the global setter blink::WebView::SetUseExternalPopupMenus(false) to get Chrome to render popup menus in the renderer instead of externally on macOS, into a command-line renderer flag --offscreen which does the same thing, except at render thread startup time, which is where Chromium sets the flag: https://chromium.googlesource.com/chromium/src/+/refs/tags/75.0.3755.3/content/renderer/render_thread_impl.cc#728.

This was the last usage of RenderViewObserver in our codebase, so this PR also removes that class.

atom/renderer/atom_autofill_agent.h

@@ -9,7 +9,6 @@
 
 #include "base/memory/weak_ptr.h"
 #include "content/public/renderer/render_frame_observer.h"
-#include "content/public/renderer/render_view_observer.h"
 #include "third_party/blink/public/web/web_autofill_client.h"
 #include "third_party/blink/public/web/web_form_control_element.h"
 #include "third_party/blink/public/web/web_input_element.h"

atom/renderer/atom_render_view_observer.cc

@@ -1,37 +0,0 @@
-// Copyright (c) 2013 GitHub, Inc.
-// Use of this source code is governed by the MIT license that can be
-// found in the LICENSE file.
-
-#include "atom/renderer/atom_render_view_observer.h"
-
-#include "atom/common/api/api_messages.h"
-#include "content/public/renderer/render_view.h"
-#include "ipc/ipc_message_macros.h"
-#include "third_party/blink/public/web/web_view.h"
-
-namespace atom {
-
-AtomRenderViewObserver::AtomRenderViewObserver(content::RenderView* render_view)
-    : content::RenderViewObserver(render_view) {}
-
-AtomRenderViewObserver::~AtomRenderViewObserver() {}
-
-bool AtomRenderViewObserver::OnMessageReceived(const IPC::Message& message) {
-  bool handled = true;
-  IPC_BEGIN_MESSAGE_MAP(AtomRenderViewObserver, message)
-    IPC_MESSAGE_HANDLER(AtomViewMsg_Offscreen, OnOffscreen)
-    IPC_MESSAGE_UNHANDLED(handled = false)
-  IPC_END_MESSAGE_MAP()
-
-  return handled;
-}
-
-void AtomRenderViewObserver::OnDestruct() {
-  delete this;
-}
-
-void AtomRenderViewObserver::OnOffscreen() {
-  blink::WebView::SetUseExternalPopupMenus(false);
-}
-
-}  // namespace atom

atom/renderer/atom_render_view_observer.h

@@ -1,31 +0,0 @@
-// Copyright (c) 2013 GitHub, Inc.
-// Use of this source code is governed by the MIT license that can be
-// found in the LICENSE file.
-
-#ifndef ATOM_RENDERER_ATOM_RENDER_VIEW_OBSERVER_H_
-#define ATOM_RENDERER_ATOM_RENDER_VIEW_OBSERVER_H_
-
-#include "content/public/renderer/render_view_observer.h"
-
-namespace atom {
-
-class AtomRenderViewObserver : public content::RenderViewObserver {
- public:
-  explicit AtomRenderViewObserver(content::RenderView* render_view);
-
- protected:
-  ~AtomRenderViewObserver() override;
-
- private:
-  // content::RenderViewObserver implementation.
-  bool OnMessageReceived(const IPC::Message& message) override;
-  void OnDestruct() override;
-
-  void OnOffscreen();
-
-  DISALLOW_COPY_AND_ASSIGN(AtomRenderViewObserver);
-};
-
-}  // namespace atom
-
-#endif  // ATOM_RENDERER_ATOM_RENDER_VIEW_OBSERVER_H_

atom/renderer/renderer_client_base.cc

@@ -13,13 +13,13 @@
 #include "atom/common/options_switches.h"
 #include "atom/renderer/atom_autofill_agent.h"
 #include "atom/renderer/atom_render_frame_observer.h"
-#include "atom/renderer/atom_render_view_observer.h"
 #include "atom/renderer/content_settings_observer.h"
 #include "atom/renderer/electron_api_service_impl.h"
 #include "atom/renderer/preferences_manager.h"
 #include "base/command_line.h"
 #include "base/strings/string_split.h"
 #include "base/strings/stringprintf.h"
+#include "content/common/buildflags.h"
 #include "content/public/common/content_constants.h"
 #include "content/public/common/content_switches.h"
 #include "content/public/renderer/render_frame.h"
@@ -142,6 +142,15 @@ void RendererClientBase::AddRenderBindings(
 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.
+  if (command_line->HasSwitch(options::kOffscreen)) {
+    blink::WebView::SetUseExternalPopupMenus(false);
+  }
+#endif
+
   blink::WebCustomElement::AddEmbedderCustomElementName("webview");
   blink::WebCustomElement::AddEmbedderCustomElementName("browserplugin");
 
@@ -252,10 +261,6 @@ void RendererClientBase::RenderFrameCreated(
   }
 }
 
-void RendererClientBase::RenderViewCreated(content::RenderView* render_view) {
-  new AtomRenderViewObserver(render_view);
-}
-
 void RendererClientBase::DidClearWindowObject(
     content::RenderFrame* render_frame) {
   // Make sure every page will get a script context created.

atom/renderer/renderer_client_base.h

@@ -54,7 +54,6 @@ class RendererClientBase : public content::ContentRendererClient {
   // content::ContentRendererClient:
   void RenderThreadStarted() override;
   void RenderFrameCreated(content::RenderFrame*) override;
-  void RenderViewCreated(content::RenderView*) override;
   std::unique_ptr<blink::WebSpeechSynthesizer> OverrideSpeechSynthesizer(
       blink::WebSpeechSynthesizerClient* client) override;
   bool OverrideCreatePlugin(content::RenderFrame* render_frame,