Add tests for DocumentsContract/Provider.

Confirm that invoking methods on DocumentsContract will correctly
be decoded and passed through to a DocumentsProvider instance.

Bug: 123725500, 123660195
Test: atest android.provider.cts.DocumentsContractTest
Change-Id: I16e7da808db83645db06f16a6be2c9575d9a3d06
diff --git a/core/java/android/content/ContentProvider.java b/core/java/android/content/ContentProvider.java
index f138d39..e06322df 100644
--- a/core/java/android/content/ContentProvider.java
+++ b/core/java/android/content/ContentProvider.java
@@ -134,7 +134,7 @@
     private boolean mNoPerms;
     private boolean mSingleUser;
 
-    private final ThreadLocal<String> mCallingPackage = new ThreadLocal<>();
+    private ThreadLocal<String> mCallingPackage;
 
     private Transport mTransport = new Transport();
 
@@ -2034,6 +2034,7 @@
 
     private void attachInfo(Context context, ProviderInfo info, boolean testing) {
         mNoPerms = testing;
+        mCallingPackage = new ThreadLocal<>();
 
         /*
          * Only allow it to be set once, so after the content service gives