Installed theme only available in one window

[kieferrm]

• VSCode Version: Code - Insiders 1.17.0-insider (81fc22e, 2017-10-03T23:17:52.245Z)
• OS Version: Windows_NT x64 10.0.16362
• Extensions:

Extension	Author (truncated)	Version
vsc-material-theme	Equ	1.0.4

(1 theme extensions excluded)

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Steps to Reproduce:

1. Open two workspaces
2. In one of the windows install a new theme
3. Reload Window
4. Change theme to newly installed theme
   -> the other window still has the old theme, when you want to change to the new theme explicitly, it's not in the list of available themes

This behavior is different from when I re-launch VS Code with the theme already installed. All theme changes are taking affect across all windows.

Reproduces without extensions: Yes/No

[sandy081]

This is because, every window has its own extension host. We need to reload the window when a new extension is installed and for the extension to take effect.

[sandy081]

Duplicate of #5675