As of today, we create `PageTarget` instances whenever we get a
sync IPC from the content process. This, however, breaks an invariant
that `browserContext.pages` always has all pages (and *browsing contexts* - not to be confused with *browser contexts*), associated with browser context. This invariant will be especially important when we move
user agent emulation to browser-side.
This patch makes `PageTarget` lifecycle symmetrical:
- `PageTarget` instance is created when tab is opened
- `PageTarget` is destroyed when tab is crashed or closed
This should also fix a bunch of race conditions with persistent mode, since sometimes we arrive to the window after its
initialization.
Drive-by: straighten viewport management and put a nice descriptive comment.
Juggler code had a bug where we subscribed to window and tab
events, but did not iterate collections of current windows and tabs.
As a result, we were sometimes failing to set viewport size for the
initial window, and implemented an artificial promise to workaround
the problem.
This patch:
- starts calling `onOpenWindow` and `onOpenTabListener` callbacks
for *all* windows and tabs - current and future, eliminating the
race condition.
This worked too well and we started overriding window sizes that
were set by users with `window.open(url, 'width=300;height=400')` (we
have a test for this). To fix this, we now plumb `CHROME_WITH_SIZE`
flag from appWindow and override viewport iff this flag is not set.
After this patch, we will use the `onTabOpened` event to move user
agent emulation to the browser-side.
References #3995
