Adding margin height for transient taskbar to allow users to stash taskbar from full height.

Test: visual(video in buganizer)
Fix: 263526574
Change-Id: I21fd1273b83a4e5efdf7aeacae1303513b9b4d97
diff --git a/quickstep/src/com/android/launcher3/taskbar/TaskbarStashController.java b/quickstep/src/com/android/launcher3/taskbar/TaskbarStashController.java
index c269648..6031b49 100644
--- a/quickstep/src/com/android/launcher3/taskbar/TaskbarStashController.java
+++ b/quickstep/src/com/android/launcher3/taskbar/TaskbarStashController.java
@@ -364,7 +364,12 @@
      * Returns the height that taskbar will be touchable.
      */
     public int getTouchableHeight() {
-        return mIsStashed ? mStashedHeight : mUnstashedHeight;
+        int bottomMargin = 0;
+        if (DisplayController.isTransientTaskbar(mActivity)) {
+            bottomMargin = mActivity.getResources().getDimensionPixelSize(
+                    R.dimen.transient_taskbar_margin);
+        }
+        return mIsStashed ? mStashedHeight : (mUnstashedHeight + bottomMargin);
     }
 
     /**