Add unittest for percentage width inside absolute layout

Summary:
Added unittest to constraint layout of percentage width inside absolute parent. See #454.
Closes https://github.com/facebook/yoga/pull/456

Differential Revision: D4674103

Pulled By: emilsjolander

fbshipit-source-id: 569a762e5a2b4ac80cd79bfbc9abfe57ada74dc9

gentest/fixtures/YGPercentageTest.html

@@ -100,3 +100,10 @@
     </div>
   </div>
 </div>
+
+<div id="percent_absolute_position" style="width: 60px; height: 50px;">
+  <div style="height: 50px; width: 100%; left: 50%; position: absolute; flex-direction: row;">
+    <div style="width: 100%;"></div>
+    <div style="width: 100%;"></div>
+  </div>
+</div>