Make the dump of the window hierarchy more readable

Activities weren't indented, making it hard to read.

Test: dumpsys window -a
Change-Id: Ibd39bd34ac128caf67eb07c932913a9078de9439
diff --git a/services/core/java/com/android/server/wm/Task.java b/services/core/java/com/android/server/wm/Task.java
index 7d970d9..2e86351 100644
--- a/services/core/java/com/android/server/wm/Task.java
+++ b/services/core/java/com/android/server/wm/Task.java
@@ -687,11 +687,12 @@
         pw.println(doublePrefix + "mTempInsetBounds=" + mTempInsetBounds.toShortString());
 
         final String triplePrefix = doublePrefix + "  ";
+        final String quadruplePrefix = triplePrefix + "  ";
 
         for (int i = mChildren.size() - 1; i >= 0; i--) {
             final AppWindowToken wtoken = mChildren.get(i);
             pw.println(triplePrefix + "Activity #" + i + " " + wtoken);
-            wtoken.dump(pw, triplePrefix, dumpAll);
+            wtoken.dump(pw, quadruplePrefix, dumpAll);
         }
     }