Add a gray debug line to NSSL to show the keyguard padding.

Bug: 190630151
Test: Disable the keyguard max; add 5 normal notifications on a sargo, see them all draw right up to the gray line.  Replace 1 with a conversation (adds a few dp padding) and see the shelf appear.  Soo.. seems consistent.
Change-Id: Id5f93b7151dd0b1698ceebda9a01c592ba54bb2f

packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/NotificationStackScrollLayout.java

@@ -413,6 +413,7 @@ public class NotificationStackScrollLayout extends ViewGroup implements Dumpable
     private boolean mBackwardScrollable;
     private NotificationShelf mShelf;
     private int mMaxDisplayedNotifications = -1;
+    private float mKeyguardBottomPadding = -1;
     private int mStatusBarHeight;
     private int mMinInteractionHeight;
     private final Rect mClipRect = new Rect();
@@ -738,6 +739,16 @@ public class NotificationStackScrollLayout extends ViewGroup implements Dumpable
             mDebugPaint.setColor(Color.YELLOW);
             canvas.drawLine(0, y, getWidth(), y, mDebugPaint);
 
+            y = (int) mMaxLayoutHeight;
+            mDebugPaint.setColor(Color.MAGENTA);
+            canvas.drawLine(0, y, getWidth(), y, mDebugPaint);
+
+            if (mKeyguardBottomPadding >= 0) {
+                y = getHeight() - (int) mKeyguardBottomPadding;
+                mDebugPaint.setColor(Color.GRAY);
+                canvas.drawLine(0, y, getWidth(), y, mDebugPaint);
+            }
+
             y = getHeight() - getEmptyBottomMargin();
             mDebugPaint.setColor(Color.GREEN);
             canvas.drawLine(0, y, getWidth(), y, mDebugPaint);
@@ -4773,6 +4784,16 @@ public class NotificationStackScrollLayout extends ViewGroup implements Dumpable
         }
     }
 
+    /**
+     * This is used for debugging only; it will be used to draw the otherwise invisible line which
+     * NotificationPanelViewController treats as the bottom when calculating how many notifications
+     * appear on the keyguard.
+     * Setting a negative number will disable rendering this line.
+     */
+    public void setKeyguardBottomPadding(float keyguardBottomPadding) {
+        mKeyguardBottomPadding = keyguardBottomPadding;
+    }
+
     @ShadeViewRefactor(RefactorComponent.SHADE_VIEW)
     public void setShouldShowShelfOnly(boolean shouldShowShelfOnly) {
         mShouldShowShelfOnly = shouldShowShelfOnly;

packages/SystemUI/src/com/android/systemui/statusbar/notification/stack/NotificationStackScrollLayoutController.java

@@ -1204,6 +1204,16 @@ public class NotificationStackScrollLayoutController {
         mNotificationListContainer.setMaxDisplayedNotifications(maxNotifications);
     }
 
+    /**
+     * This is used for debugging only; it will be used to draw the otherwise invisible line which
+     * NotificationPanelViewController treats as the bottom when calculating how many notifications
+     * appear on the keyguard.
+     * Setting a negative number will disable rendering this line.
+     */
+    public void setKeyguardBottomPadding(float keyguardBottomPadding) {
+        mView.setKeyguardBottomPadding(keyguardBottomPadding);
+    }
+
     public RemoteInputController.Delegate createDelegate() {
         return new RemoteInputController.Delegate() {
             public void setRemoteInputActive(NotificationEntry entry,

packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationPanelViewController.java

@@ -325,6 +325,8 @@ public class NotificationPanelViewController extends PanelViewController {
     private final LockscreenShadeTransitionController mLockscreenShadeTransitionController;
     private final TapAgainViewController mTapAgainViewController;
     private boolean mShouldUseSplitNotificationShade;
+    // The bottom padding reserved for elements of the keyguard measuring notifications
+    private float mKeyguardNotificationBottomPadding;
     // Current max allowed keyguard notifications determined by measuring the panel
     private int mMaxAllowedKeyguardNotifications;
 
@@ -1169,9 +1171,12 @@ public class NotificationPanelViewController extends PanelViewController {
         if (mKeyguardShowing && !mKeyguardBypassController.getBypassEnabled()) {
             mNotificationStackScrollLayoutController.setMaxDisplayedNotifications(
                     mMaxAllowedKeyguardNotifications);
+            mNotificationStackScrollLayoutController.setKeyguardBottomPadding(
+                    mKeyguardNotificationBottomPadding);
         } else {
             // no max when not on the keyguard
             mNotificationStackScrollLayoutController.setMaxDisplayedNotifications(-1);
+            mNotificationStackScrollLayoutController.setKeyguardBottomPadding(-1f);
         }
     }
 
@@ -1353,6 +1358,7 @@ public class NotificationPanelViewController extends PanelViewController {
 
         float bottomPadding = Math.max(mIndicationBottomPadding, mAmbientIndicationBottomPadding);
         bottomPadding = Math.max(lockIconPadding, bottomPadding);
+        mKeyguardNotificationBottomPadding = bottomPadding;
 
         float availableSpace =
                 mNotificationStackScrollLayoutController.getHeight()