Ensure the EXTRA_SHOW_TAB is checked for all new intents.

onNewIntent is only called when the activity is already active so when
an intent is sent to start the DialtactsActivity on a specific tab when
the DialtactsActivity is not already active, the code to switch to the
specific tab is not called. Move this code to onResume() instead.

Bug: 21120186
Change-Id: I735eae22ca5de54f4c17688777b4309616f2c691