Show spinner while waiting for mutations.

When mutation operations are waiting for a storage backend, show a
spinner in place of the save button.

Bug: 11333249
Change-Id: I2b620b4532ad977a2b60d4bdc5caa55f89021456
diff --git a/src/com/android/documentsui/CreateDirectoryFragment.java b/src/com/android/documentsui/CreateDirectoryFragment.java
index 90be197..ba8c35f 100644
--- a/src/com/android/documentsui/CreateDirectoryFragment.java
+++ b/src/com/android/documentsui/CreateDirectoryFragment.java
@@ -95,6 +95,11 @@
         }
 
         @Override
+        protected void onPreExecute() {
+            mActivity.setPending(true);
+        }
+
+        @Override
         protected DocumentInfo doInBackground(Void... params) {
             final ContentResolver resolver = mActivity.getContentResolver();
             ContentProviderClient client = null;
@@ -120,6 +125,8 @@
             } else {
                 Toast.makeText(mActivity, R.string.create_error, Toast.LENGTH_SHORT).show();
             }
+
+            mActivity.setPending(false);
         }
     }
 }