Expose screen metrics and window metrics

Summary:
public
https://github.com/facebook/react-native/pull/4935 changed the window dimensions for android by replacing them with the actual screen dimensions. This changes the window dimensions back to their original values and adds `Dimensions.get('screen')` for the actual screen dimensions of the device.

Reviewed By: astreet

Differential Revision: D2921584

fb-gh-sync-id: 5d2677029c71d50691691dc651a11e9c8b115e8f
shipit-source-id: 5d2677029c71d50691691dc651a11e9c8b115e8f

ReactAndroid/src/main/java/com/facebook/react/uimanager/PixelUtil.java

@@ -23,7 +23,7 @@ public class PixelUtil {
     return TypedValue.applyDimension(
         TypedValue.COMPLEX_UNIT_DIP,
         value,
-        DisplayMetricsHolder.getDisplayMetrics());
+        DisplayMetricsHolder.getWindowDisplayMetrics());
   }
 
   /**
@@ -40,7 +40,7 @@ public class PixelUtil {
     return TypedValue.applyDimension(
         TypedValue.COMPLEX_UNIT_SP,
         value,
-        DisplayMetricsHolder.getDisplayMetrics());
+        DisplayMetricsHolder.getWindowDisplayMetrics());
   }
 
   /**
@@ -54,7 +54,7 @@ public class PixelUtil {
    * Convert from PX to DP
    */
   public static float toDIPFromPixel(float value) {
-    return value / DisplayMetricsHolder.getDisplayMetrics().density;
+    return value / DisplayMetricsHolder.getWindowDisplayMetrics().density;
   }
 
 }