Session wide preload script

[zcbenz]

As per #2522, it would be good to allow setting preload script for all pages under the same session, so child windows opened by window.open can also be managed.

[inca]

Is there any work planned for this? I'm interested in session-wide preload scripts particularly because of #5115, having this implemented would allow one to interact with iframes and child windows without disabling web security.

[codebytere]

Closing on merge of #10430

[iffy]

@codebytere so is 10430 in a released version of electron?

[carsonwright]

@codebytere based on the creators of #10430 it appears that they do not intend to create support for iframes all others will be supported but not iframes.