[vm/isolate] Avoid isolate scan when exiting known isolate.

IsolateFibonacci before 3291867, after 3061103

Fixes #50789
TEST=benchmark/IsolateFibonacci

Change-Id: I667838c4ae089b9ac8889ae3eb3d773115437397
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/276760
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Alexander Aprelev <aam@google.com>

Author: aam

runtime/lib/isolate.cc

@@ -351,12 +351,14 @@ DEFINE_NATIVE_ENTRY(Isolate_exit_, 0, 2) {
     handle->set_ptr(msg_array);
     isolate->bequeath(std::unique_ptr<Bequest>(new Bequest(handle, port.Id())));
   }
-  Isolate::KillIfExists(isolate, Isolate::LibMsgId::kKillMsg);
-  // Drain interrupts before running so any IMMEDIATE operations on the current
-  // isolate happen synchronously.
-  const Error& error = Error::Handle(thread->HandleInterrupts());
-  RELEASE_ASSERT(error.IsUnwindError());
+
+  Thread::Current()->StartUnwindError();
+  const String& msg =
+      String::Handle(String::New("isolate terminated by Isolate.exit"));
+  const UnwindError& error = UnwindError::Handle(UnwindError::New(msg));
+  error.set_is_user_initiated(true);
   Exceptions::PropagateError(error);
+  UNREACHABLE();
   // We will never execute dart code again in this isolate.
   return Object::null();
 }

runtime/vm/dart_api_impl_test.cc

@@ -775,7 +775,7 @@ void Func1() {
 
   result = Dart_Invoke(lib, NewString("Func1"), 0, NULL);
   EXPECT(Dart_IsError(result));
-  EXPECT_SUBSTRING("isolate terminated by Isolate.kill", Dart_GetError(result));
+  EXPECT_SUBSTRING("isolate terminated by Isolate.exit", Dart_GetError(result));
 
   result = Dart_Invoke(lib, NewString("Func1"), 0, NULL);
   EXPECT(Dart_IsError(result));