Implement fromEnvironment on bool, int and String

runtime/vm/isolate.h

Index: runtime/vm/isolate.h
diff --git a/runtime/vm/isolate.h b/runtime/vm/isolate.h
index f42247e34824fbaa4c40cd7069c7e777c0e1e2a1..bd3d0be33bc5a355f8de60439e7c24946492f8b7 100644
--- a/runtime/vm/isolate.h
+++ b/runtime/vm/isolate.h
@@ -174,6 +174,13 @@ class Isolate : public BaseIsolate {
     return init_callback_data_;
   }
 
+  Dart_EnvironmentCallback environment_callback() const {
+    return environment_callback_;
+  }
+  void set_environment_callback(Dart_EnvironmentCallback value) {
+    environment_callback_ = value;
+  }
+
   Dart_LibraryTagHandler library_tag_handler() const {
     return library_tag_handler_;
   }
@@ -393,6 +400,7 @@ class Isolate : public BaseIsolate {
   RawContext* top_context_;
   uword top_exit_frame_info_;
   void* init_callback_data_;
+  Dart_EnvironmentCallback environment_callback_;
   Dart_LibraryTagHandler library_tag_handler_;
   ApiState* api_state_;
   StubCode* stub_code_;