Make it easier to create asynchronous Handlers.

There are potentially very many Handlers owned by services
that should not be blocked by barriers introduced by UI traversals
occurring on the same thread (if that ever happens).
Add some convenience constructors to make it easy to switch
these Handlers over to being async.

Bug: 7057752
Change-Id: I64d9bffe81e7c52ada4cfad4e89d4340153f4688
diff --git a/services/java/com/android/server/DockObserver.java b/services/java/com/android/server/DockObserver.java
index 2bed957..f1ff27f 100644
--- a/services/java/com/android/server/DockObserver.java
+++ b/services/java/com/android/server/DockObserver.java
@@ -241,7 +241,7 @@
                 SCREENSAVER_ACTIVATE_ON_DOCK, DEFAULT_SCREENSAVER_ACTIVATED_ON_DOCK) != 0;
     }
 
-    private final Handler mHandler = new Handler(Looper.myLooper(), null, true) {
+    private final Handler mHandler = new Handler(true /*async*/) {
         @Override
         public void handleMessage(Message msg) {
             switch (msg.what) {