display audio dialog when connecting low end dock

Display a dialog to enable the use of the dock audio connection
when a low end dock is connected for the first time.

Modify DockService to process docked and undocked messages even if
the device indicated is null (meaning the dock is not a bluetooth dock)
only for low end docks.

Bug 7302106.

Change-Id: I331d83a74fecf5f26b24bfc178342df414bd8153

res/layout/dock_audio_media_enable_dialog.xml

@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (C) 2012 The Android Open Source Project
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<CheckBox
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:id="@+id/dock_audio_media_enable_cb"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:text="@string/bluetooth_dock_settings_a2dp"
+    android:focusable="true"
+    android:clickable="true" />