Support updated rendering of conversation icons.

Note that changes to channel settings now generate
onResume() for all available controllers to ensure they get
the updated drawable.

Bug: 149747760
Change-Id: I3f73c025b1d32194e3d5147d03cb781e370f2a1b
Test: make -j64 RunSettingsRoboTests ROBOTEST_FILTER="com.android.settings.notification"

src/com/android/settings/widget/EntityHeaderController.java

@@ -135,7 +135,8 @@ public class EntityHeaderController {
      */
     public EntityHeaderController setIcon(Drawable icon) {
         if (icon != null) {
-            mIcon = icon.getConstantState().newDrawable(mAppContext.getResources());
+            final Drawable.ConstantState state = icon.getConstantState();
+            mIcon = state != null ? state.newDrawable(mAppContext.getResources()) : icon;
         }
         return this;
     }