Add battery indicator to bluetooth icon

This cl change util method in bluetooth package to return
drawable instead of resId.

If the bt device has battery level, then method return customized
layerDrawable, otherwise return a simple drawable created from
resId.

Bug: 63393322
Test: RunSettingsRoboTests

Change-Id: Ib21822eafda0e8570212ce5cb070478e4f4876a2
Merged-In: Ib21822eafda0e8570212ce5cb070478e4f4876a2

src/com/android/settings/bluetooth/BluetoothDevicePreference.java

@@ -21,6 +21,7 @@ import android.bluetooth.BluetoothDevice;
 import android.content.Context;
 import android.content.DialogInterface;
 import android.content.res.Resources;
+import android.graphics.drawable.Drawable;
 import android.os.UserManager;
 import android.support.v7.preference.Preference;
 import android.support.v7.preference.PreferenceViewHolder;
@@ -120,9 +121,9 @@ public final class BluetoothDevicePreference extends GearPreference implements
         // Null check is done at the framework
         setSummary(mCachedDevice.getConnectionSummary());
 
-        Pair<Integer, String> pair = Utils.getBtClassDrawableWithDescription(mResources,
+        final Pair<Drawable, String> pair = Utils.getBtClassDrawableWithDescription(getContext(),
                 mCachedDevice);
-        if (pair.first != 0) {
+        if (pair.first != null) {
             setIcon(pair.first);
             contentDescription = pair.second;
         }