Do not set the content description on the icon tab when not necessary

It is not necessary to set the content description of a tab's icon
when the icon is not actually visible. Based on the implementation,
the tab's icon is only visible when not null and its visibility is
set to true.

Change-Id: I4430dfc7d1faa0ae00fdc789745e7cae7b453a89
fix some CTS problems

Some CTS test cases which are to test a long-click availability on a
view fail if "long_press_timeout" would be changed. For instance, if
we would change "Touch & hold delay" setting to "medium" or "long",
the following test cases fail.
  - GestureDetectorTest#testOnTouchEvent
  - View_UsingViewsTest#testSetupListeners
  - AbsListViewTest#testGetContextMenuInfo
These test cases call TouchUtils.longClickView(). ThelongClickView()
uses ViewConfiguration.getLongPressTimeout() to get
"long_press_timeout". However the method will always return a
default value '500' if it would be called from non-main thread.
CTS test case runs on non-main thread. So longClickView() should
read the value from SettingProvider.

Change-Id: I19465678a1f6a10b93262263975d612b386856f9