Create base MapBuffer class and tests

Summary: This diff creates the base classes for MapBuffer and its tests

Reviewed By: shergin

Differential Revision: D15550730

fbshipit-source-id: a5a47edebd7c3e1b8b2c3ad2006aee0f8bdb7866

Author: mdvacca

ReactCommon/fabric/mapbuffer/MapBuffer.cpp

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+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include "MapBuffer.h"
+
+namespace facebook {
+namespace react {
+
+MapBuffer::MapBuffer() {}
+
+MapBuffer::~MapBuffer() {}
+
+} // namespace react
+} // namespace facebook

ReactCommon/fabric/mapbuffer/MapBuffer.h

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+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <string>
+
+namespace facebook {
+namespace react {
+
+/**
+ * MapBuffer is an optimized map format for transferring data like props between
+ * C++ and other platforms The implemenation of this map is optimized to:
+ * - be compact to optimize space when sparse (sparse is the common case).
+ * - be accessible through JNI with zero/minimal copying via ByteBuffer.
+ * - be Have excellent C++ single-write and many-read performance by maximizing
+ *   CPU cache performance through compactness, data locality, and fixed offsets
+ *   where possible.
+ * - be optimized for iteration and intersection against other maps, but with
+ *   reasonably good random access as well.
+ * - Work recursively for nested maps/arrays.
+ * - Supports dynamic types that map to JSON.
+ * - Don't require mutability - single-write on creation.
+ * - have minimal APK size and build time impact.
+ */
+class MapBuffer {
+ public:
+  MapBuffer();
+  virtual ~MapBuffer();
+};
+
+} // namespace react
+} // namespace facebook

ReactCommon/fabric/mapbuffer/tests/MapBufferTest.cpp

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+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#include <memory>
+
+#include <gtest/gtest.h>
+
+TEST(MapBufferTest, testSomething) {
+  // TODO
+}