Replace usages of hexToRgb with setNormalizedColorAlpha

Reviewed By: vjeux

Differential Revision: D2906507

fb-gh-sync-id: 671ec5b9f5a701891c3601a8f78968b99476a2b5
shipit-source-id: 671ec5b9f5a701891c3601a8f78968b99476a2b5

Libraries/StyleSheet/setNormalizedColorAlpha.js

@@ -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.
+ *
+ * @providesModule setNormalizedColorAlpha
+ * @flow
+ */
+/* eslint no-bitwise: 0 */
+'use strict';
+
+/**
+ * number should be a color processed by `normalizeColor`
+ * alpha should be number between 0 and 1
+ */
+function setNormalizedColorAlpha(input: number, alpha: number): number {
+  if (alpha < 0) {
+    alpha = 0;
+  } else if (alpha > 1) {
+    alpha = 1;
+  }
+
+  alpha = Math.round(alpha * 255);
+  // magic bitshift guarantees we return an unsigned int
+  return ((input & 0xffffff00) | alpha) >>> 0;
+}
+
+module.exports = setNormalizedColorAlpha;