Build failure on Ubuntu about agera HOT 6 CLOSED

diff --git a/agera/src/main/java/com/google/android/agera/BaseObservable.java b/agera/src/main/java/com/google/android/agera/BaseObservable.java
index 4938fd1..396cec0 100644
--- a/agera/src/main/java/com/google/android/agera/BaseObservable.java
+++ b/agera/src/main/java/com/google/android/agera/BaseObservable.java
@@ -15,9 +15,6 @@
  */
 package com.google.android.agera;

-import static com.google.android.agera.Common.WorkerHandler.MSG_LAST_REMOVED;
-import static com.google.android.agera.Common.WorkerHandler.MSG_UPDATE;
-import static com.google.android.agera.Common.workerHandler;
 import static com.google.android.agera.Preconditions.checkState;

 import com.google.android.agera.Common.WorkerHandler;
@@ -97,16 +94,16 @@ public abstract class BaseObservable implements Observable {

     Worker(@NonNull final BaseObservable baseObservable) {
       this.baseObservable = baseObservable;
-      this.handler = workerHandler();
+      this.handler = Common.workerHandler();
       this.updatablesAndHandlers = NO_UPDATABLES_OR_HANDLERS;
       this.size = 0;
     }

     synchronized void addUpdatable(@NonNull final Updatable updatable) {
-      add(updatable, workerHandler());
+      add(updatable, Common.workerHandler());
       if (size == 1) {
-        if (handler.hasMessages(MSG_LAST_REMOVED, this)) {
-          handler.removeMessages(MSG_LAST_REMOVED, this);
+        if (handler.hasMessages(Common.WorkerHandler.MSG_LAST_REMOVED, this)) {
+          handler.removeMessages(Common.WorkerHandler.MSG_LAST_REMOVED, this);
         } else {
           handler.obtainMessage(WorkerHandler.MSG_FIRST_ADDED, this).sendToTarget();
         }
@@ -116,13 +113,13 @@ public abstract class BaseObservable implements Observable {
     synchronized void removeUpdatable(@NonNull final Updatable updatable) {
       remove(updatable);
       if (size == 0) {
-        handler.obtainMessage(MSG_LAST_REMOVED, this).sendToTarget();
+        handler.obtainMessage(Common.WorkerHandler.MSG_LAST_REMOVED, this).sendToTarget();
       }
     }

     void dispatchUpdate() {
-      if (!handler.hasMessages(MSG_UPDATE, this)) {
-        handler.obtainMessage(MSG_UPDATE, this).sendToTarget();
+      if (!handler.hasMessages(Common.WorkerHandler.MSG_UPDATE, this)) {
+        handler.obtainMessage(Common.WorkerHandler.MSG_UPDATE, this).sendToTarget();
       }
     }