Fix 5288804: Make music trasports in lockscreen more closely match design

This fixes three issues;
- Make the background black while the transport is showing.
- Show scrim sandwiched between artwork and overlapping UI.
- Remove gaps in sides of background assets.

Change-Id: I563fc680c4c042d8b25ec37332aeab528cf838ca

core/res/res/layout/keyguard_transport_control.xml

@@ -19,23 +19,28 @@
      but rather as include tags for this file or the layout will break. -->
 <com.android.internal.widget.TransportControlView
     xmlns:android="http://schemas.android.com/apk/res/android"
-    android:id="@+id/transport_controls"
-    android:background="@drawable/ic_lockscreen_player_background">
+    android:id="@+id/transport_controls">
 
-    <ImageView
-        android:id="@+id/albumart"
+    <!-- FrameLayout used as scrim to show between album art and buttons -->
+    <FrameLayout
         android:layout_width="match_parent"
         android:layout_height="match_parent"
-        android:layout_gravity="fill"
-        android:scaleType="centerCrop"
-        android:adjustViewBounds="false"
+        android:foreground="@drawable/ic_lockscreen_player_background">
+        <!-- We use ImageView for its cropping features, otherwise could be android:background -->
+        <ImageView
+            android:id="@+id/albumart"
+            android:layout_width="match_parent"
+            android:layout_height="match_parent"
+            android:layout_gravity="fill"
+            android:scaleType="centerCrop"
+            android:adjustViewBounds="false"
         />
+    </FrameLayout>
 
     <LinearLayout
         android:orientation="vertical"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
-        android:background="#c8000000"
         android:layout_gravity="bottom">
         <TextView
             android:id="@+id/title"