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/AbstractDrawCommand.java

@@ -0,0 +1,108 @@
+/**
+ * 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;
+
+/**
+ * Base class for all DrawCommands. Becomes immutable once it has its bounds set. Until then, a
+ * subclass is able to mutate any of its properties (e.g. updating Layout in DrawTextLayout).
+ *
+ * The idea is to be able to reuse unmodified objects when we build up DrawCommands before we ship
+ * them to UI thread, but we can only do that if DrawCommands are immutable.
+ */
+/* package */ abstract class AbstractDrawCommand implements DrawCommand, Cloneable {
+
+  private float mLeft;
+  private float mTop;
+  private float mRight;
+  private float mBottom;
+  private boolean mFrozen;
+
+  /**
+   * Updates boundaries of the AbstractDrawCommand and freezes it.
+   * Will return a frozen copy if the current AbstractDrawCommand cannot be mutated.
+   */
+  public final AbstractDrawCommand updateBoundsAndFreeze(
+      float left,
+      float top,
+      float right,
+      float bottom) {
+    if (mFrozen) {
+      // see if we can reuse it
+      if (boundsMatch(left, top, right, bottom)) {
+        return this;
+      }
+
+      try {
+        AbstractDrawCommand copy = (AbstractDrawCommand) clone();
+        copy.setBounds(left, top, right, bottom);
+        return copy;
+      } catch (CloneNotSupportedException e) {
+        // This should not happen since AbstractDrawCommand implements Cloneable
+        throw new RuntimeException(e);
+      }
+    }
+
+    setBounds(left, top, right, bottom);
+    mFrozen = true;
+    return this;
+  }
+
+  /**
+   * Returns whether this object was frozen and thus cannot be mutated.
+   */
+  public final boolean isFrozen() {
+    return mFrozen;
+  }
+
+  /**
+   * Left position of this DrawCommand relative to the hosting View.
+   */
+  public final float getLeft() {
+    return mLeft;
+  }
+
+  /**
+   * Top position of this DrawCommand relative to the hosting View.
+   */
+  public final float getTop() {
+    return mTop;
+  }
+
+  /**
+   * Right position of this DrawCommand relative to the hosting View.
+   */
+  public final float getRight() {
+    return mRight;
+  }
+
+  /**
+   * Bottom position of this DrawCommand relative to the hosting View.
+   */
+  public final float getBottom() {
+    return mBottom;
+  }
+
+  /**
+   * Updates boundaries of this DrawCommand.
+   */
+  private void setBounds(float left, float top, float right, float bottom) {
+    mLeft = left;
+    mTop = top;
+    mRight = right;
+    mBottom = bottom;
+  }
+
+  /**
+   * Returns true if boundaries match and don't need to be updated. False otherwise.
+   */
+  private boolean boundsMatch(float left, float top, float right, float bottom) {
+    return mLeft == left && mTop == top && mRight == right && mBottom == bottom;
+  }
+}