Reducing the number of recent tasks we keep.

- This should decrease the time it takes to fetch the recent task list,
  and also reduce the number of tasks we store on-disk.
- Since a user can still open a fair number of tasks within the 
  time-window, and this list includes tasks that are excluded from the 
  UI, we are just reducing it to about half for the time being.

Bug: 28318359
Change-Id: Ie21b3d3d09a567007015fbbecaf914123c71cc06

core/java/android/app/ActivityManager.java

@@ -901,7 +901,7 @@ public class ActivityManager {
      */
     static public int getMaxRecentTasksStatic() {
         if (gMaxRecentTasks < 0) {
-            return gMaxRecentTasks = isLowRamDeviceStatic() ? 50 : 100;
+            return gMaxRecentTasks = isLowRamDeviceStatic() ? 36 : 48;
         }
         return gMaxRecentTasks;
     }