Applying tinyify to plotly.js crashes Node

I'm trying to optimize a bundle that contains the (rather hefty) [plotly.js](https://github.com/plotly/plotly.js) library.

When I pass `-p tinyify` to my bundling command it will hang for quite a while and then crash, printing the following:

```
<--- Last few GCs --->

[9631:0x36f27f0] 56924 ms: Mark-sweep 1345.1 (1440.5) -> 1344.3 (1456.5) MB, 1270.8 / 0.0 ms (average mu = 0.103, current mu = 0.006) allocation failure scavenge might not succeed
[9631:0x36f27f0] 58143 ms: Mark-sweep 1344.3 (1456.5) -> 1344.3 (1456.5) MB, 1218.0 / 0.0 ms (average mu = 0.053, current mu = 0.000) allocation failure GC in old space requested

<--- JS stacktrace --->

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

0: ExitFrame [pc: 0x292a09adc01d]
Security context: 0x37fbe811e549
1: addHelpers [0x1401217d54e9] [/home/frederik/projects/tinyify-crash/node_modules/transform-ast/index.js:~87] [pc=0x292a0a5a7f5a](this=0x2f3e1e21aa09 ,node=0x071fba8d11c1 )
2: enter [0x208cdc2350f9] [/home/frederik/projects/tinyify-crash/node_modules/transform-ast/index.js:~33] [pc=0x292a09e5713a](this=0x2f...

FATAL ERROR: Ineffective mark-compacts near heap limit Allocation failed - JavaScript heap out of memory
1: 0x8c02c0 node::Abort() [node]
2: 0x8c030c [node]
3: 0xad15de v8::Utils::ReportOOMFailure(v8::internal::Isolate*, char const*, bool) [node]
4: 0xad1814 v8::internal::V8::FatalProcessOutOfMemory(v8::internal::Isolate*, char const*, bool) [node]
5: 0xebe752 [node]
6: 0xebe858 v8::internal::Heap::CheckIneffectiveMarkCompact(unsigned long, double) [node]
7: 0xeca982 v8::internal::Heap::PerformGarbageCollection(v8::internal::GarbageCollector, v8::GCCallbackFlags) [node]
8: 0xecb2b4 v8::internal::Heap::CollectGarbage(v8::internal::AllocationSpace, v8::internal::GarbageCollectionReason, v8::GCCallbackFlags) [node]
9: 0xecdf21 v8::internal::Heap::AllocateRawWithRetryOrFail(int, v8::internal::AllocationSpace, v8::internal::AllocationAlignment) [node]
10: 0xe96236 [node]
11: 0xea8a87 v8::internal::Factory::NewLoadHandler(int) [node]
12: 0xf2828e v8::internal::LoadHandler::LoadFullChain(v8::internal::Isolate*, v8::internal::Handle, v8::internal::Handle, v8::internal::Handle)
[node]
13: 0xf3663d v8::internal::LoadIC::UpdateCaches(v8::internal::LookupIterator*) [node]
14: 0xf36b6c v8::internal::LoadIC::Load(v8::internal::Handle, v8::internal::Handle) [node]
15: 0xf3b4a5 v8::internal::Runtime_LoadIC_Miss(int, v8::internal::Object**, v8::internal::Isolate*) [node]
16: 0x292a09adc01d
Aborted (core dumped)
```

When I omit the plugin, I can bundle things just fine. I also can pipe the bundle through `uglifyjs --mangle` just fine.

I created a repo with an example case here: https://github.com/m90/tinyify-crash

As for Node internals, I am running the following on Ubuntu 16:

```
➜ ~ node -v
v10.9.0
➜ ~ npm -v
6.4.0
```

Bắt đầu bằng cách chạy repository ví dụ tại https://github.com/m90/tinyify-crash với thiết lập Node v10.9.0 đã được báo cáo, sau đó kiểm tra node_modules/transform-ast/index.js quanh addHelpers và so sánh tinyify với pipeline uglifyjs đang hoạt động. Được xem là hoàn tất khi bundle Plotly.js hoàn thành với tinyify mà không bị treo hoặc làm cạn heap của Node.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.