Unpersisted webviews being kept around when editor restarts

[mjbvz]

Issue Type: Bug

Steps

1. Run Show release notes
2. Reload window

Bug
Empty release notes tab still around after start

VS Code version: Code - Insiders 1.33.0-insider (4d1cb56, 2019-04-03T08:11:05.447Z)
OS version: Darwin x64 18.2.0

System Info

Item	Value
CPUs	Intel(R) Core(TM) i7-4770HQ CPU @ 2.20GHz (8 x 2200)
GPU Status	2d_canvas: enabled checker_imaging: disabled_off flash_3d: enabled flash_stage3d: enabled flash_stage3d_baseline: enabled gpu_compositing: enabled multiple_raster_threads: enabled_on native_gpu_memory_buffers: enabled rasterization: enabled surface_synchronization: enabled_on video_decode: enabled webgl: enabled webgl2: enabled
Load (avg)	3, 3, 3
Memory (System)	16.00GB (0.63GB free)
Process Argv	-psn_0_19132990
Screen Reader	no
VM	22%

[mjbvz]

Fixed by 06dd68b in master

[rebornix]

Another way to verify:

• Open a description view for a pull request from GH PR extension
• Reload the window

[mjbvz]

Fixed in 1.33 branch with #71689