Add two panel home support for page binding logic

There's a logic which prioritizes the binding for the
current page and defers the other pages' binding.
If two panel home is enabled, we want to bind both pages
together. LauncherPageRestoreHelper has been created to
contain the logic for persisting restoring and calculating
which pages to load immediately.

Test: manual + run LauncherPageRestoreHelperTest robo test
Bug: 174464691
Change-Id: I57ac3f7150303b95b272e922f44bda26f9d5ce2a

src/com/android/launcher3/util/IntArray.java

@@ -17,13 +17,14 @@
 package com.android.launcher3.util;
 
 import java.util.Arrays;
+import java.util.Iterator;
 import java.util.StringTokenizer;
 
 /**
  * Copy of the platform hidden implementation of android.util.IntArray.
  * Implements a growing array of int primitives.
  */
-public class IntArray implements Cloneable {
+public class IntArray implements Cloneable, Iterable<Integer> {
     private static final int MIN_CAPACITY_INCREMENT = 12;
 
     private static final int[] EMPTY_INT = new int[0];
@@ -272,4 +273,30 @@ public class IntArray implements Cloneable {
             throw new ArrayIndexOutOfBoundsException("length=" + len + "; index=" + index);
         }
     }
+
+    @Override
+    public Iterator<Integer> iterator() {
+        return new ValueIterator();
+    }
+
+    @Thunk
+    class ValueIterator implements Iterator<Integer> {
+
+        private int mNextIndex = 0;
+
+        @Override
+        public boolean hasNext() {
+            return mNextIndex < size();
+        }
+
+        @Override
+        public Integer next() {
+            return get(mNextIndex++);
+        }
+
+        @Override
+        public void remove() {
+            throw new UnsupportedOperationException();
+        }
+    }
 }