[Qt][MiniBrowser] Improve the update of touch indicators
https://bugs.webkit.org/show_bug.cgi?id=111429

Reviewed by Jocelyn Turcotte.

MiniBrowserApplication::sendTouchEvent sends an empty list
to BrowserWindow::updateVisualMockTouchPoints if the control
button is released, in which case the touch indicators should
be hidden so that we never end up with a leftover indicator
sticking on the screen.
This patch also simplifies the lookup of the indicator items by
replacing the findChild search in the item tree with a QHash
that stores the touch ID's and the pointers to the corresponding
indicator items.

* MiniBrowser/qt/BrowserWindow.cpp:
(BrowserWindow::updateVisualMockTouchPoints):
* MiniBrowser/qt/BrowserWindow.h:
(BrowserWindow):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144758 268f45cc-cd09-0410-ab3c-d52691b4dbfc