Fix inspector to become alive when application resumes from a --start-paused.

[terrylucas]

DevTools correctly handles --start-paused to resume all isolates that are paused. Also fixes exceptions when isWidget, etc. are called and Flutter is paused on start (see PR).

After the application resumed (switch Debugger tab and press 'Resume' button).

Then switch to the inspector tab notice the inspector does not correctly load the widget tree (even after the 'Refresh Tree' is pressed).

The inspector needs to properly reconnect when Flutter is running again.