fix(chromium): fix a race between Page.enable and Page.getFrameTree

[dgozman]

We send Page.enable before Page.getFrameTree. That means we could receive Page.frameNavigated event after Page.enable response but before Page.getFrameTree response, at the point where main frame is not initialized yet.

To fix this, we can ignore any events from the Page domain which arrive before Page.getFrameTree response. Since no other domain is enabled yet, we can move all event handlers together.

Here is a failure stack trace:

  TypeError: Cannot read property 'childFrames' of undefined
      at FrameManager.frameCommittedNewDocumentNavigation (/home/runner/work/playwright/playwright/src/frames.ts:112:11)
      at CRPage._onFrameNavigated (/home/runner/work/playwright/playwright/src/chromium/crPage.ts:173:3)
      at CRSession.CRPage._eventListeners.helper_1.helper.addEventListener.event (/home/runner/work/playwright/playwright/src/chromium/crPage.ts:75:75)
      at CRSession.emit (events.js:189:13)
      at Promise.resolve.then (/home/runner/work/playwright/playwright/src/chromium/crConnection.ts:165:5)
      at process._tickCallback (internal/process/next_tick.js:68:7)