Expose userActivityTimeout through @SystemApi getter/setter.

This reverts commit 0dad572090.
System api documentation is not updated under PDK builds.

Change-Id: I851bcd66e0b764265e69ac104d5604bf316d5d10

api/system-current.txt

@@ -36913,8 +36913,10 @@ package android.view {
     method public java.lang.String debug(java.lang.String);
     method public int describeContents();
     method public final java.lang.CharSequence getTitle();
+    method public final long getUserActivityTimeout();
     method public static boolean mayUseInputMethod(int);
     method public final void setTitle(java.lang.CharSequence);
+    method public final void setUserActivityTimeout(long);
     method public void writeToParcel(android.os.Parcel, int);
     field public static final int ALPHA_CHANGED = 128; // 0x80
     field public static final int ANIMATION_CHANGED = 16; // 0x10

core/java/android/view/WindowManager.java

@@ -16,6 +16,7 @@
 
 package android.view;
 
+import android.annotation.SystemApi;
 import android.app.Presentation;
 import android.content.Context;
 import android.content.pm.ActivityInfo;
@@ -1590,7 +1591,19 @@ public interface WindowManager extends ViewManager {
         public final CharSequence getTitle() {
             return mTitle;
         }
-    
+
+        /** @hide */
+        @SystemApi
+        public final void setUserActivityTimeout(long timeout) {
+            userActivityTimeout = timeout;
+        }
+
+        /** @hide */
+        @SystemApi
+        public final long getUserActivityTimeout() {
+            return userActivityTimeout;
+        }
+
         public int describeContents() {
             return 0;
         }