Empty JavaScriptFrameIterator while executing script

[Shivan]

I'm working on a research project that adds instrumentation code to Blink and V8. As part of that instrumentation, I want to get the script ID of the currently executing script from the Isolate while the script is executing, and how I'm doing this is (in isolate.cc):

```

int Isolate::GetScriptId() {

JavaScriptFrameIterator it(this);

while (!it.done()) {

JavaScriptFrame* frame = it.frame();

Handle<JSFunction> function(frame->function(), this);

Object maybe_script = function->shared().script();

if (!maybe_script.IsScript()) {

  it.Advance();

  continue;

}

Script script = Script::cast(maybe_script);

return script.id();

}

}

```

Then I call this from various places in Blink code. One such place is `StorageArea::getItem` (third_party/blink/renderer/modules/storage/storage_area.cc) to record which script called getItem. 

This normally works fine, but for one particular script on one particular website, I get an empty stack (i.e. JavaScriptFrameIterator `it.done()` is true right after instantiation). This is the output of `PrintStack(stdout, Isolate::kPrintStackConcise)`:

```

==== JS stack trace =========================================

    0: ExitFrame [pc: 0x10f5993bf]

    1: StubFrame [pc: 0x10f6dbf1b]

Security context: 0x001e08333019 <String[#47]: https://hbr.org978B69E968F091D0A4963181648E7306>

    2: /* anonymous */(aka /* anonymous */) [0x1e081af4c9](this=0x001e0804030d <undefined>,0x001e08b4ee41 <Storage map = 0x1e082e6191>#0#)

    3: StubFrame [pc: 0x10f6d8894]

    4: StubFrame [pc: 0x10f40b328]

    5: EntryFrame [pc: 0x10f371d58]

=====================

```

I realize this is a bit involved: and relates to both Blink and V8, just wondering if anyone knows why this might be the case or have any tips for debugging.