Do not register UI-related native functions in secondary isolates (#6401)

Fixes https://github.com/flutter/flutter/issues/22478

lib/ui/dart_ui.cc

@@ -35,6 +35,7 @@ namespace blink {
 namespace {
 
 static tonic::DartLibraryNatives* g_natives;
+static tonic::DartLibraryNatives* g_natives_secondary;
 
 Dart_NativeFunction GetNativeFunction(Dart_Handle name,
                                       int argument_count,
@@ -42,10 +43,21 @@ Dart_NativeFunction GetNativeFunction(Dart_Handle name,
   return g_natives->GetNativeFunction(name, argument_count, auto_setup_scope);
 }
 
+Dart_NativeFunction GetNativeFunctionSecondary(Dart_Handle name,
+                                               int argument_count,
+                                               bool* auto_setup_scope) {
+  return g_natives_secondary->GetNativeFunction(name, argument_count,
+                                                auto_setup_scope);
+}
+
 const uint8_t* GetSymbol(Dart_NativeFunction native_function) {
   return g_natives->GetSymbol(native_function);
 }
 
+const uint8_t* GetSymbolSecondary(Dart_NativeFunction native_function) {
+  return g_natives_secondary->GetSymbol(native_function);
+}
+
 }  // namespace
 
 void DartUI::InitForGlobal() {
@@ -73,13 +85,20 @@ void DartUI::InitForGlobal() {
     SemanticsUpdateBuilder::RegisterNatives(g_natives);
     Vertices::RegisterNatives(g_natives);
     Window::RegisterNatives(g_natives);
+
+    // Secondary isolates do not provide UI-related APIs.
+    g_natives_secondary = new tonic::DartLibraryNatives();
+    DartRuntimeHooks::RegisterNatives(g_natives_secondary);
   }
 }
 
-void DartUI::InitForIsolate() {
+void DartUI::InitForIsolate(bool is_root_isolate) {
   FML_DCHECK(g_natives);
+  auto get_native_function =
+      is_root_isolate ? GetNativeFunction : GetNativeFunctionSecondary;
+  auto get_symbol = is_root_isolate ? GetSymbol : GetSymbolSecondary;
   DART_CHECK_VALID(Dart_SetNativeResolver(Dart_LookupLibrary(ToDart("dart:ui")),
-                                          GetNativeFunction, GetSymbol));
+                                          get_native_function, get_symbol));
 }
 
 }  // namespace blink

lib/ui/dart_ui.h

@@ -12,7 +12,7 @@ namespace blink {
 class DartUI {
  public:
   static void InitForGlobal();
-  static void InitForIsolate();
+  static void InitForIsolate(bool is_root_isolate);
 
  private:
   FML_DISALLOW_IMPLICIT_CONSTRUCTORS(DartUI);

runtime/dart_isolate.cc

@@ -243,7 +243,7 @@ bool DartIsolate::LoadLibraries(bool is_root_isolate) {
 
   DartIO::InitForIsolate();
 
-  DartUI::InitForIsolate();
+  DartUI::InitForIsolate(is_root_isolate);
 
   const bool is_service_isolate = Dart_IsServiceIsolate(isolate());