Make ArrayMap.EMPTY immutable

This is a regression from KitKat.

Bug:19271657
Change-Id: I11b8e4dd50f6a8d2b15fef66b44aa2d72b1f0349

core/java/android/util/ArrayMap.java

@@ -255,7 +255,10 @@ public final class ArrayMap<K, V> implements Map<K, V> {
     }
 
     private ArrayMap(boolean immutable) {
-        mHashes = EmptyArray.INT;
+        // If this is immutable, use the sentinal EMPTY_IMMUTABLE_INTS
+        // instance instead of the usual EmptyArray.INT. The reference
+        // is checked later to see if the array is allowed to grow.
+        mHashes = immutable ? EMPTY_IMMUTABLE_INTS : EmptyArray.INT;
         mArray = EmptyArray.OBJECT;
         mSize = 0;
     }