Eliminate groupId and add task to AppWindowToken

Simplifies access by eliminating indirect referencing.

Fixes bug 18088522 item #15.

Change-Id: I9049192a7f3e1028d60c4f2d4d4a0d4aad590aa4
diff --git a/services/core/java/com/android/server/wm/DisplayContent.java b/services/core/java/com/android/server/wm/DisplayContent.java
index e3b53b0..8bbc5a9 100644
--- a/services/core/java/com/android/server/wm/DisplayContent.java
+++ b/services/core/java/com/android/server/wm/DisplayContent.java
@@ -379,7 +379,7 @@
             ArrayList<Task> tasks = stack.getTasks();
             for (int taskNdx = tasks.size() - 1; taskNdx >= 0; --taskNdx) {
                 final Task task = tasks.get(taskNdx);
-                pw.print("    mTaskId="); pw.println(task.taskId);
+                pw.print("    mTaskId="); pw.println(task.mTaskId);
                 AppTokenList tokens = task.mAppTokens;
                 for (int tokenNdx = tokens.size() - 1; tokenNdx >= 0; --tokenNdx, ++ndx) {
                     final AppWindowToken wtoken = tokens.get(tokenNdx);