RN: Fix YellowBox Layout Bug

Summary:
Looks like a recent change in Yoga causes the height of an absolutely positioned fullscreen view to break.

This works around the issue by using the newly introduced percentage `height` instead.

Reviewed By: jingc

Differential Revision: D4530240

fbshipit-source-id: 86d758576c6984686f30d7504e11f9ec3ce469bd

Libraries/ReactNative/YellowBox.js

@@ -240,7 +240,7 @@ const WarningInspector = ({
         <Text style={styles.inspectorCountText}>{countSentence}</Text>
         <TouchableHighlight onPress={toggleStacktrace} underlayColor="transparent">
           <Text style={styles.inspectorButtonText}>
-            {stacktraceVisible ? '▼' : '▶' } Stacktrace
+            {stacktraceVisible ? '\u{25BC}' : '\u{25B6}'} Stacktrace
           </Text>
         </TouchableHighlight>
       </View>
@@ -396,17 +396,12 @@ const rowHeight = 46;
 
 var styles = StyleSheet.create({
   fullScreen: {
-    backgroundColor: 'transparent',
-    position: 'absolute',
-    left: 0,
-    right: 0,
-    top: 0,
-    bottom: 0,
+    height: '100%',
     elevation: Number.MAX_VALUE
   },
   inspector: {
     backgroundColor: backgroundColor(0.95),
-    flex: 1,
+    height: '100%',
     paddingTop: 5,
     elevation: Number.MAX_VALUE
   },
@@ -459,9 +454,7 @@ var styles = StyleSheet.create({
     elevation: Number.MAX_VALUE
   },
   listRow: {
-    position: 'relative',
     backgroundColor: backgroundColor(0.95),
-    flex: 1,
     height: rowHeight,
     marginTop: rowGutter,
   },