Check DreamActivity callback type to prevent class cast exception

This keeps the type-checking introduced in http://ag/21518427, but removes the NO_HISTORY flag which causes the lowlight system dream on tablets to break

This reverts commit be56335883.

Reason for revert: fix-forward

Change-Id: Idc5ce791fb07f2a7a181fb0b875bf001968b6889

core/java/android/service/dreams/DreamActivity.java

@@ -58,11 +58,13 @@ public class DreamActivity extends Activity {
             setTitle(title);
         }
 
-        final Bundle extras = getIntent().getExtras();
-        mCallback = (DreamService.DreamActivityCallbacks) extras.getBinder(EXTRA_CALLBACK);
-
-        if (mCallback != null) {
+        final Object callback = getIntent().getExtras().getBinder(EXTRA_CALLBACK);
+        if (callback instanceof DreamService.DreamActivityCallbacks) {
+            mCallback = (DreamService.DreamActivityCallbacks) callback;
             mCallback.onActivityCreated(this);
+        } else {
+            mCallback = null;
+            finishAndRemoveTask();
         }
     }