Add top offset for react loading view on Kitkat

Summary:
This PR fixes the problem with dev loading view on KitKat and older Android devices after #16596

Install RNTester app on Android API 19 or lower device. See green loading view show up under status bar. Do the same with full screen theme set and see it show up correctly at the top of the screen.
Verify the green loading bar displays correctly on devices with API > 19 too.

This fixes an issue introduced in #16596

[ANDROID][MINOR][DevSupport] - Fix green dev loading bar on Android Kitkat and below
Closes #17305

Differential Revision: D6621077

Pulled By: achen1

fbshipit-source-id: 3b4216af535d7db5c96d137f20004fe2651b1dc9

Author: kmagiera

ReactAndroid/src/main/java/com/facebook/react/devsupport/DevLoadingViewController.java

@@ -12,9 +12,12 @@
 import android.app.Activity;
 import android.content.Context;
 import android.graphics.Color;
+import android.graphics.Rect;
+import android.os.Build;
 import android.view.Gravity;
 import android.view.LayoutInflater;
 import android.view.ViewGroup;
+import android.view.Window;
 import android.widget.PopupWindow;
 import android.widget.TextView;
 
@@ -53,7 +56,7 @@ public DevLoadingViewController(Context context, ReactInstanceManagerDevHelper r
   }
 
   public void showMessage(final String message, final int color, final int backgroundColor) {
-    if (!sEnabled ) {
+    if (!sEnabled) {
       return;
     }
 
@@ -147,6 +150,16 @@ private void showInternal() {
       return;
     }
 
+    int topOffset = 0;
+    if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.KITKAT) {
+      // On Android SDK <= 19 PopupWindow#showAtLocation uses absolute screen position. In order for
+      // loading view to be placed below status bar (if the status bar is present) we need to pass
+      // an appropriate Y offset.
+      Rect rectangle = new Rect();
+      currentActivity.getWindow().getDecorView().getWindowVisibleDisplayFrame(rectangle);
+      topOffset = rectangle.top;
+    }
+
     mDevLoadingPopup = new PopupWindow(
             mDevLoadingView,
             ViewGroup.LayoutParams.MATCH_PARENT,
@@ -156,8 +169,9 @@ private void showInternal() {
     mDevLoadingPopup.showAtLocation(
             currentActivity.getWindow().getDecorView(),
             Gravity.NO_GRAVITY,
+
             0,
-            0);
+            topOffset);
   }
 
   private void hideInternal() {