Move CancellationSignal to android.os package.

Bug: 6427830
Change-Id: I39451bb1e1d4a8d976ed1c671234f0c8c61658dd
diff --git a/core/java/android/content/ContentProvider.java b/core/java/android/content/ContentProvider.java
index 1206056..b22179e 100644
--- a/core/java/android/content/ContentProvider.java
+++ b/core/java/android/content/ContentProvider.java
@@ -29,6 +29,9 @@
 import android.os.AsyncTask;
 import android.os.Binder;
 import android.os.Bundle;
+import android.os.CancellationSignal;
+import android.os.ICancellationSignal;
+import android.os.OperationCanceledException;
 import android.os.ParcelFileDescriptor;
 import android.os.Process;
 import android.os.RemoteException;