Add SHOW_INPUT_METHOD_PICKER broadcast test

The CL [1] introduced a protected-broadcast intent action for internal
use. This CL ensures that the protected-broadcast intent can't be
invoked by non-system user.

 [1]: Id36c8c34159bea8b72557b40bcf024d401f580b6

Bug: 63644555
Test: Passed CTS permission2 test.
    $ cts-tradefed run singleCommand cts-dev \
          -m CtsPermission2TestCases \
	  -t android.permission2.cts.ProtectedBroadcastsTest
Test: Confirmed the following command causes error.
    $ adb shell am broadcast \
          -a com.android.server.InputMethodManagerService.SHOW_INPUT_METHOD_PICKER
    java.lang.SecurityException: Permission Denial: not allowed to send
    broadcast com.android.server.InputMethodManagerService.SHOW_INPUT_METHOD_PICKER
    from pid=xxxx, uid=xxxx
Change-Id: Ib58d2931cc8db3b88eab64352ba445be67eaec68
diff --git a/tests/tests/permission2/src/android/permission2/cts/ProtectedBroadcastsTest.java b/tests/tests/permission2/src/android/permission2/cts/ProtectedBroadcastsTest.java
index 534481e..37b9461 100644
--- a/tests/tests/permission2/src/android/permission2/cts/ProtectedBroadcastsTest.java
+++ b/tests/tests/permission2/src/android/permission2/cts/ProtectedBroadcastsTest.java
@@ -81,7 +81,8 @@
         "android.net.wifi.p2p.PERSISTENT_GROUPS_CHANGED",
         "android.net.conn.TETHER_STATE_CHANGED",
         "android.net.conn.INET_CONDITION_ACTION",
-        "android.net.conn.CAPTIVE_PORTAL_TEST_COMPLETED"
+        "android.net.conn.CAPTIVE_PORTAL_TEST_COMPLETED",
+        "com.android.server.InputMethodManagerService.SHOW_INPUT_METHOD_PICKER"
     };
 
     /**