RN: Android Constants for Overflow Style

Summary:
Tidies up the hardcoded strings for referencing the `overflow` style values.

Also, the `OVERFLOW` case in the optimized view flattening code path is unnecessary because `OVERFLOW` is already in the `LAYOUT_ONLY_PROPS` set.

Reviewed By: achen1

Differential Revision: D8690804

fbshipit-source-id: 3befbe93ed761e57e45f9b50e59bffc8a29a407f

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

@@ -74,6 +74,9 @@ public class ViewProps {
   public static final String MIN_HEIGHT = "minHeight";
   public static final String MAX_HEIGHT = "maxHeight";
 
+  public static final String HIDDEN = "hidden";
+  public static final String VISIBLE = "visible";
+
   public static final String ASPECT_RATIO = "aspectRatio";
 
   // Props that sometimes may prevent us from collapsing views
@@ -254,8 +257,6 @@ public static boolean isLayoutOnly(ReadableMap map, String prop) {
           return map.isNull(BORDER_RIGHT_WIDTH) || map.getDouble(BORDER_RIGHT_WIDTH) == 0d;
         case BORDER_BOTTOM_WIDTH:
           return map.isNull(BORDER_BOTTOM_WIDTH) || map.getDouble(BORDER_BOTTOM_WIDTH) == 0d;
-        case OVERFLOW: // We do nothing with this right now.
-          return true;
         default:
           return false;
       }

ReactAndroid/src/main/java/com/facebook/react/views/view/ReactViewGroup.java

@@ -37,6 +37,7 @@
 import com.facebook.react.uimanager.RootView;
 import com.facebook.react.uimanager.RootViewUtil;
 import com.facebook.react.uimanager.ViewGroupDrawingOrderHelper;
+import com.facebook.react.uimanager.ViewProps;
 import com.facebook.yoga.YogaConstants;
 import javax.annotation.Nullable;
 
@@ -682,12 +683,12 @@ protected void dispatchDraw(Canvas canvas) {
   private void dispatchOverflowDraw(Canvas canvas) {
     if (mOverflow != null) {
       switch (mOverflow) {
-        case "visible":
+        case ViewProps.VISIBLE:
           if (mPath != null) {
             mPath.rewind();
           }
           break;
-        case "hidden":
+        case ViewProps.HIDDEN:
           if (mReactBackgroundDrawable != null) {
             float left = 0f;
             float top = 0f;