Send accessibility event for content change upon setting content description.

1. Since the content description is generated dynamically we need to notify
   clients when it changes so they can drop cached state to get the most
   recent content. This really is used by the caching we do to optimize
   the window query APIs. Otherwise, the user does not see the current
   content.

bug:7327556

Change-Id: I9be46508e86864566e027c64565eb1d787ec9363

Author: sganov

core/java/android/view/View.java

@@ -5214,11 +5214,19 @@ public CharSequence getContentDescription() {
      */
     @RemotableViewMethod
     public void setContentDescription(CharSequence contentDescription) {
+        if (mContentDescription == null) {
+            if (contentDescription == null) {
+                return;
+            }
+        } else if (mContentDescription.equals(contentDescription)) {
+            return;
+        }
         mContentDescription = contentDescription;
         final boolean nonEmptyDesc = contentDescription != null && contentDescription.length() > 0;
         if (nonEmptyDesc && getImportantForAccessibility() == IMPORTANT_FOR_ACCESSIBILITY_AUTO) {
              setImportantForAccessibility(IMPORTANT_FOR_ACCESSIBILITY_YES);
         }
+        notifyAccessibilityStateChanged();
     }
 
     /**