Add MtpDocumentsService.

BUG=20274999

Change-Id: I1d60ebcf100767136ac7f78e619021776c6be02f
diff --git a/packages/MtpDocumentsProvider/AndroidManifest.xml b/packages/MtpDocumentsProvider/AndroidManifest.xml
index 6172354..c1848c7 100644
--- a/packages/MtpDocumentsProvider/AndroidManifest.xml
+++ b/packages/MtpDocumentsProvider/AndroidManifest.xml
@@ -2,6 +2,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
           package="com.android.mtp"
           android:sharedUserId="android.media">
+    <uses-feature android:name="android.hardware.usb.host" />
     <application android:label="@string/app_label">
         <provider
             android:name=".MtpDocumentsProvider"
@@ -14,5 +15,6 @@
                 <action android:name="android.content.action.DOCUMENTS_PROVIDER" />
             </intent-filter>
         </provider>
+        <service android:name=".MtpDocumentsService"></service>
     </application>
 </manifest>