Revert "Allow views to setSystemUiVisibility() with the same value and have it work."

This reverts commit fad9555217.
Because it just didn't work. (The views kept aggressively
re-applying their preferred flags every time view attributes
were aggregated.)

We'll pursue the original strategy, like lights out mode in
HC: if you want to tickle this mode, un-set and re-set the
flags (preferably synchronized with the global SystemUI
visibility state as reported by onSystemUiVisibilityChanged
callbacks).

Bug: 5052456

core/java/android/view/View.java

@@ -12969,15 +12969,13 @@ public class View implements Drawable.Callback, Drawable.Callback2, KeyEvent.Cal
      * Request that the visibility of the status bar be changed.
      * @param visibility  Bitwise-or of flags {@link #SYSTEM_UI_FLAG_LOW_PROFILE} or
      * {@link #SYSTEM_UI_FLAG_HIDE_NAVIGATION}.
-     *
-     * This value will be re-applied immediately, even if the flags have not changed, so a view may
-     * easily reassert a particular SystemUiVisibility condition even if the system UI itself has
-     * since countermanded the original request.
      */
     public void setSystemUiVisibility(int visibility) {
-        mSystemUiVisibility = visibility;
-        if (mParent != null && mAttachInfo != null && !mAttachInfo.mRecomputeGlobalAttributes) {
-            mParent.recomputeViewAttributes(this);
+        if (visibility != mSystemUiVisibility) {
+            mSystemUiVisibility = visibility;
+            if (mParent != null && mAttachInfo != null && !mAttachInfo.mRecomputeGlobalAttributes) {
+                mParent.recomputeViewAttributes(this);
+            }
         }
     }