Add snapToAlignment to ReactScrollViewManager

Summary:
This diff adds the new snapToAlignment into ReactScrollViewManager
changelog: [Android][Added] Implement snapToAlignment into ReactScrollViewManager

Reviewed By: JoshuaGross

Differential Revision: D31182787

fbshipit-source-id: 8049ceb462461a11f184dbc1b40ca8079a3e8b60

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.java

@@ -7,6 +7,8 @@
 
 package com.facebook.react.views.scroll;
 
+import static com.facebook.react.views.scroll.ReactScrollViewHelper.SNAP_ALIGNMENT_DISABLED;
+
 import android.animation.Animator;
 import android.animation.ObjectAnimator;
 import android.animation.PropertyValuesHolder;
@@ -92,6 +94,7 @@ public class ReactScrollView extends ScrollView
   private @Nullable List<Integer> mSnapOffsets;
   private boolean mSnapToStart = true;
   private boolean mSnapToEnd = true;
+  private int mSnapToAlignment = SNAP_ALIGNMENT_DISABLED;
   private @Nullable View mContentView;
   private ReactViewBackgroundManager mReactBackgroundManager;
   private int pendingContentOffsetX = UNSET_CONTENT_OFFSET;
@@ -218,6 +221,10 @@ public class ReactScrollView extends ScrollView
     mSnapToEnd = snapToEnd;
   }
 
+  public void setSnapToAlignment(int snapToAlignment) {
+    mSnapToAlignment = snapToAlignment;
+  }
+
   public void flashScrollIndicators() {
     awakenScrollBars();
   }

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewManager.java

@@ -115,6 +115,11 @@ public class ReactScrollViewManager extends ViewGroupManager<ReactScrollView>
     view.setSnapOffsets(offsets);
   }
 
+  @ReactProp(name = "snapToAlignment")
+  public void setSnapToAlignment(ReactScrollView view, String alignment) {
+    view.setSnapToAlignment(ReactScrollViewHelper.parseSnapToAlignment(alignment));
+  }
+
   @ReactProp(name = "snapToStart")
   public void setSnapToStart(ReactScrollView view, boolean snapToStart) {
     view.setSnapToStart(snapToStart);