Fix Array Index out of bounds error.

This error was caused by concurrent modification of the
mPendingNotifications SparseIntArray which fell outside the
synchronization block in copyAndNotifyListeners. Now the entire
copyAndNotifyListeners is synchronized on mLock.

Bug: b/37775443
Test: runtest --path
frameworks/base/packages/SettingsLib/tests/integ/src/com/android/settingslib/wifi/WifiTrackerTest.java

Change-Id: I19e8a4ecea5cd45122f4ca89f8ed959e500c951a