A basic POT 2D allocator

This 2D allocator only supports power-of-two, square allocations. It
uses a quadtree to store the allocated regions.

The quadtree implementation currently has a fixed depth (templated).

The allocator does a best-fit match, but currently doesn't implement a
free method.

libs/utils/test/test_QuadTreeArray.cpp

@@ -0,0 +1,43 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <gtest/gtest.h>
+
+#include <utils/QuadTree.h>
+
+using namespace utils;
+
+TEST(QuadTreeArrayTest, TraversalDFS) {
+
+    using QuadTree = QuadTreeArray<bool, 4>;
+    QuadTree qt;
+    QuadTree::NodeId indices[qt.size()];
+
+    QuadTree::traverse(0, 0,
+            [&](auto const& curr) -> QuadTree::TraversalResult {
+                size_t i = QuadTreeUtils::index(curr.l, curr.code);
+                indices[i] = curr;
+                return QuadTree::TraversalResult::RECURSE;
+            });
+
+    size_t i = 0;
+    for (size_t y = 0; y < QuadTree::height(); y++) {
+        for (size_t x = 0; x < (1 << 2 * y); x++, i++) {
+            EXPECT_EQ(indices[i].l, y);
+            EXPECT_EQ(indices[i].code, x);
+        }
+    }
+}