Explicitly export content providers

In a future version of Android, the default value for
<provider android:exported> will change from true to false.
Explicitly set android:exported="true"

Bug: 3306452
Change-Id: Ic5d3152988ed6a576501830338ec324f056921c4
diff --git a/AndroidManifest.xml b/AndroidManifest.xml
index 09056cf..2b89dca 100644
--- a/AndroidManifest.xml
+++ b/AndroidManifest.xml
@@ -240,6 +240,7 @@
         <provider android:name="com.android.gallery3d.provider.GalleryProvider"
                 android:syncable="false"
                 android:grantUriPermissions="true"
+                android:exported="true"
                 android:authorities="com.android.gallery3d.provider" />
         <activity android:name="com.android.gallery3d.gadget.WidgetClickHandler" />
         <activity android:name="com.android.gallery3d.app.DialogPicker"