Restricting DocumentsProvider#getType by implementing getTypeAnonymous

- getTypeAnonymous can be accessed by anyone. It does not reveal any sensitive information.

Bug: b/271262541
Test: build and manual test
Change-Id: I300a3be0904c44214f3ab206c30314855feaa57b

core/api/current.txt

@@ -36849,6 +36849,7 @@ package android.provider {
     method public String[] getDocumentStreamTypes(String, String);
     method public String getDocumentType(String) throws java.io.FileNotFoundException;
     method public final String getType(android.net.Uri);
+    method @Nullable public final String getTypeAnonymous(@NonNull android.net.Uri);
     method public final android.net.Uri insert(android.net.Uri, android.content.ContentValues);
     method public boolean isChildDocument(String, String);
     method public String moveDocument(String, String, String) throws java.io.FileNotFoundException;

core/java/android/provider/DocumentsProvider.java

@@ -978,6 +978,19 @@ public abstract class DocumentsProvider extends ContentProvider {
         }
     }
 
+    /**
+     * An unrestricted version of getType, which does not reveal sensitive information
+     */
+    @Override
+    public final @Nullable String getTypeAnonymous(@NonNull Uri uri) {
+        switch (mMatcher.match(uri)) {
+            case MATCH_ROOT:
+                return DocumentsContract.Root.MIME_TYPE_ITEM;
+            default:
+                return null;
+        }
+    }
+
     /**
      * Implementation is provided by the parent class. Can be overridden to
      * provide additional functionality, but subclasses <em>must</em> always