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/UIManagerModuleConstants.java

@@ -91,7 +91,8 @@ import com.facebook.react.uimanager.events.TouchEventType;
                 "ScaleAspectFill",
                 ImageView.ScaleType.CENTER_CROP.ordinal())));
 
-    DisplayMetrics displayMetrics = DisplayMetricsHolder.getDisplayMetrics();
+    DisplayMetrics displayMetrics = DisplayMetricsHolder.getWindowDisplayMetrics();
+    DisplayMetrics screenDisplayMetrics = DisplayMetricsHolder.getScreenDisplayMetrics();
     constants.put(
         "Dimensions",
         MapBuilder.of(
@@ -106,7 +107,19 @@ import com.facebook.react.uimanager.events.TouchEventType;
                 "fontScale",
                 displayMetrics.scaledDensity,
                 "densityDpi",
-                displayMetrics.densityDpi)));
+                displayMetrics.densityDpi),
+        "screenPhysicalPixels",
+        MapBuilder.of(
+            "width",
+            screenDisplayMetrics.widthPixels,
+            "height",
+            screenDisplayMetrics.heightPixels,
+            "scale",
+            screenDisplayMetrics.density,
+            "fontScale",
+            screenDisplayMetrics.scaledDensity,
+            "densityDpi",
+            screenDisplayMetrics.densityDpi)));
 
     constants.put(
         "StyleConstants",