Text layout in switch may be null when accessibility events are fired.

1. The layout containing the text of a Switch is initialized on measure
   and if an accessibility event is fired before that then a NPE happens.

bug:7169419

Change-Id: Iee3c01ca9157d14d228c4ff33c0810507e0e25a7

Author: sganov

core/java/android/widget/Switch.java

@@ -508,9 +508,9 @@ public void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
     @Override
     public void onPopulateAccessibilityEvent(AccessibilityEvent event) {
         super.onPopulateAccessibilityEvent(event);
-        CharSequence text = isChecked() ? mOnLayout.getText() : mOffLayout.getText();
-        if (!TextUtils.isEmpty(text)) {
-            event.getText().add(text);
+        Layout layout =  isChecked() ? mOnLayout : mOffLayout;
+        if (layout != null && !TextUtils.isEmpty(layout.getText())) {
+            event.getText().add(layout.getText());
         }
     }