Add support for shadows to RCTVirtualText

Summary: React provides properties to support shadows for Text, this diff implements it for Nodes.

Reviewed By: ahmedre

Differential Revision: D2817212

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

@@ -0,0 +1,74 @@
+/**
+ * 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 android.text.TextPaint;
+import android.text.style.CharacterStyle;
+
+/* package */ final class ShadowStyleSpan extends CharacterStyle {
+
+  /* package */ static final ShadowStyleSpan INSTANCE = new ShadowStyleSpan(0, 0, 0, 0, true);
+
+  private float mDx;
+  private float mDy;
+  private float mRadius;
+  private int mColor;
+  private boolean mFrozen;
+
+  private ShadowStyleSpan(float dx, float dy, float radius, int color, boolean frozen) {
+    mDx = dx;
+    mDy = dy;
+    mRadius = radius;
+    mColor = color;
+    mFrozen = frozen;
+  }
+
+  public boolean offsetMatches(float dx, float dy) {
+    return mDx == dx && mDy == dy;
+  }
+
+  public void setOffset(float dx, float dy) {
+    mDx = dx;
+    mDy = dy;
+  }
+
+  public float getRadius() {
+    return mRadius;
+  }
+
+  public void setRadius(float radius) {
+    mRadius = radius;
+  }
+
+  public int getColor() {
+    return mColor;
+  }
+
+  public void setColor(int color) {
+    mColor = color;
+  }
+
+  /* package */ ShadowStyleSpan mutableCopy() {
+    return new ShadowStyleSpan(mDx, mDy, mRadius, mColor, false);
+  }
+
+  /* package */ boolean isFrozen() {
+    return mFrozen;
+  }
+
+  /* package */ void freeze() {
+    mFrozen = true;
+  }
+
+  @Override
+  public void updateDrawState(TextPaint textPaint) {
+    textPaint.setShadowLayer(mRadius, mDx, mDy, mColor);
+  }
+}