Fixing crash when trying to set thumbnail info.

- The TaskThumbnailInfo can have the same lifecycle as the TaskRecord, and
  we should just reset it instead of setting it to null when the thumbnail
  is disposed.

Bug: 25652261
Change-Id: I54384e208b19e60d469bf3471dd555f78f04290c

core/java/android/app/ActivityManager.java

@@ -1558,6 +1558,16 @@ public class ActivityManager {
             readFromParcel(source);
         }
 
+        /**
+         * Resets this info state to the initial state.
+         * @hide
+         */
+        public void reset() {
+            taskWidth = 0;
+            taskHeight = 0;
+            screenOrientation = 0;
+        }
+
         /** @hide */
         public void saveToXml(XmlSerializer out) throws IOException {
             out.attribute(null, ATTR_TASK_WIDTH, Integer.toString(taskWidth));

services/core/java/com/android/server/am/TaskRecord.java

@@ -572,8 +572,8 @@ final class TaskRecord {
      * Removes all associated thumbnail data when a task is removed or pruned from recents.
      */
     void disposeThumbnail() {
+        mLastThumbnailInfo.reset();
         mLastThumbnail = null;
-        mLastThumbnailInfo = null;
         lastDescription = null;
     }