StrictMode: now in more system server threads.

Who knew there were so many Loopers in the system server?

This adds dropbox logging for the activity manager thread, policy
thread, and window manager thread.

The goal's to catch more stuttering.

Change-Id: I999a6ff4a955f0ef549b12a38796b843ade5fe66
diff --git a/core/java/android/app/ContextImpl.java b/core/java/android/app/ContextImpl.java
index 5ce4cd6..ba301e9 100644
--- a/core/java/android/app/ContextImpl.java
+++ b/core/java/android/app/ContextImpl.java
@@ -1182,6 +1182,13 @@
     /* package */ static DropBoxManager createDropBoxManager() {
         IBinder b = ServiceManager.getService(DROPBOX_SERVICE);
         IDropBoxManagerService service = IDropBoxManagerService.Stub.asInterface(b);
+        if (service == null) {
+            // Don't return a DropBoxManager that will NPE upon use.
+            // This also avoids caching a broken DropBoxManager in
+            // getDropBoxManager during early boot, before the
+            // DROPBOX_SERVICE is registered.
+            return null;
+        }
         return new DropBoxManager(service);
     }