Reduce reported "Displayed activity com.android.browser/.BrowserActivity"

Reduce reported "Displayed activity com.android.browser/.BrowserActivity"
time from random 3~5s to consistent ~2.5s assuming
no apps need to be killed in the start up.

Move the faked title bar to its own Window instead
of the sub panel of the main window. This way Browser
can start when its main window is ready, instead of
waiting for both windows are ready. Also we don't
depend on mBrowserFrameLayout for the y position.
We also don't need to check decorView's window token.

Delay the fake tile bar starting time until the main
window is ready. This way we ensure the main window
will be drawn when it is ready. Otherwise the window
manager will wait until all the current windows are
ready before showing them.

Fix http://b/issue?id=2548712