browser(webkit): introduce Playwright.windowOpen protocol event

[dgozman]

dgozman/WebKit@6374ec0

[yury-s]

Can we fire this event from the WebProcess instead (it seems that both new page as well as the features are available in WebChromeClient::createWindow) and avoid all the plumbing to and in the UIProcess? Maybe generate something like Page.windowFeatures(features) in the new page as soon as its Page domain is enabled (we anyway pause it in createWindow).

[dgozman]

Can we fire this event from the WebProcess instead (it seems that both new page as well as the features are available in WebChromeClient::createWindow) and avoid all the plumbing to and in the UIProcess? Maybe generate something like Page.windowFeatures(features) in the new page as soon as its Page domain is enabled (we anyway pause it in createWindow).

I tried that first, but it was flaky. I suspect that's due to CreateWindow being a sync IPC, and sendMessageToFrontend being async one. After changing to UIProcess, the flakiness is gone.