Dynamically show the menu button on the system bar.

Windows with FLAG_NEEDS_MENU_KEY (or windowNeedsMenuKey=true
in their theme) will cause the system bar to show a menu
icon. (Note that the phone's status bar currently ignores
this, but phones tend to have hardware menu keys anyway.)

Additionally, all windows whose package's SDK version is
pre-Honeycomb will have FLAG_NEEDS_MENU_KEY set by default.

Bug: 3003728

Change-Id: I2d983763a726ea4f32cd1af9b0390e30478b11d1

core/java/android/view/WindowManager.java

@@ -611,6 +611,19 @@ public interface WindowManager extends ViewManager {
          * {@hide} */
         public static final int FLAG_SPLIT_TOUCH = 0x00800000;
 
+        /**
+         * Flag for a window belonging to an activity that responds to {@link KeyEvent#KEYCODE_MENU}
+         * and therefore needs a Menu key. For devices where Menu is a physical button this flag is
+         * ignored, but on devices where the Menu key is drawn in software it may be hidden unless
+         * this flag is set.
+         *
+         * (Note that Action Bars, when available, are the preferred way to offer additional
+         * functions otherwise accessed via an options menu.)
+         *
+         * {@hide}
+         */
+        public static final int FLAG_NEEDS_MENU_KEY = 0x01000000;
+
         /** Window flag: *sigh* The lock screen wants to continue running its
          * animation while it is fading.  A kind-of hack to allow this.  Maybe
          * in the future we just make this the default behavior.