Adds dump method to ModelDelegate.

This allows delegates to include additional data in log dumps.

Bug: 181351828
Test: Checked that data was found in a bug report and
adb shell dumpsys activity com.google.android.apps.nexuslauncher

Change-Id: I7a63430202ff899ac885a544c558e1248d2ce829

src/com/android/launcher3/LauncherModel.java

@@ -615,7 +615,9 @@ public class LauncherModel extends LauncherApps.Callback implements InstallSessi
                         + "\" bitmapIcon=" + info.bitmap.icon
                         + " componentName=" + info.componentName.getPackageName());
             }
+            writer.println();
         }
+        mModelDelegate.dump(prefix, fd, writer, args);
         mBgDataModel.dump(prefix, fd, writer, args);
     }