Sub frames should get an isolated context when node is enabled in sub frames

[samuelmaddock]

• Electron Version (output of node_modules/.bin/electron --version):
  • 5.x.x

Expected Behavior

Context isolation should be enabled in subframes when the nodeIntegrationInSubFrames option is provided.

Actual behavior

Context isolation is not enabled for node environments in subframes.

To Reproduce

Enable nodeIntegrationInSubFrames and load any content in a subframe.

Additional Information

See #16425 and https://github.com/electron/electron/blob/master/atom/renderer/atom_render_frame_observer.cc#L92-L104

I started working on a fix, but wasn't sure if the preload_bundle was actually being run in the correct context.

diff --git a/atom/renderer/atom_render_frame_observer.cc b/atom/renderer/atom_render_frame_observer.cc
index f8a54a199..b878954cc 100644
--- a/atom/renderer/atom_render_frame_observer.cc
+++ b/atom/renderer/atom_render_frame_observer.cc
@@ -12,6 +12,8 @@
 #include "atom/common/heap_snapshot.h"
 #include "atom/common/native_mate_converters/value_converter.h"
 #include "atom/common/node_includes.h"
+#include "atom/common/options_switches.h"
+#include "base/command_line.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/trace_event/trace_event.h"
@@ -95,9 +97,17 @@ void AtomRenderFrameObserver::DidCreateScriptContext(
   if (ShouldNotifyClient(world_id))
     renderer_client_->DidCreateScriptContext(context, render_frame_);
 
-  if (renderer_client_->isolated_world() && IsMainWorld(world_id) &&
-      // Only the top window's main frame has isolated world.
-      render_frame_->IsMainFrame() && !render_frame_->GetWebFrame()->Opener()) {
+  bool use_context_isolation = renderer_client_->isolated_world();
+  bool is_main_world = IsMainWorld(world_id);
+  bool is_main_frame = render_frame_->IsMainFrame();
+  bool is_not_opened = !render_frame_->GetWebFrame()->Opener();
+  bool allow_node_in_sub_frames =
+      base::CommandLine::ForCurrentProcess()->HasSwitch(
+          switches::kNodeIntegrationInSubFrames);
+  bool should_create_isolated_context =
+      use_context_isolation && (is_main_frame || allow_node_in_sub_frames) && is_main_world && is_not_opened;
+
+  if (should_create_isolated_context) {
     CreateIsolatedWorldContext();
     renderer_client_->SetupMainWorldOverrides(context, render_frame_);
   }