Add support for RCTText under FlatUIImplementation

Summary: @public Initial version of FlatUIImplementation lacks any primitives support (such as RCTText, RCTImageView or RCTView). This diff add the first part, RCTText (alongside with RCTVirtualText and RCTRawText).

Reviewed By: sriramramani

Differential Revision: D2693348

ReactAndroid/src/main/java/com/facebook/react/flat/FlatShadowNode.java

@@ -0,0 +1,31 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+package com.facebook.react.flat;
+
+import com.facebook.react.uimanager.LayoutShadowNode;
+
+/**
+ * FlatShadowNode is a base class for all shadow node used in FlatUIImplementation. It extends
+ * {@link LayoutShadowNode} by adding an ability to prepare DrawCommands off the UI thread.
+ */
+/* package */ class FlatShadowNode extends LayoutShadowNode {
+
+  /**
+   * Collects DrawCommands produced by this FlatShadoNode.
+   */
+  protected void collectState(
+      StateBuilder stateBuilder,
+      float left,
+      float top,
+      float right,
+      float bottom) {
+    // do nothing yet.
+  }
+}