Let IndividualPickerFragment indpendent from IndividualPickerActivity.

This is a preparation for switching between gallery and wallpapers.
(By replacing CategorySelectorFragment with IndividualPickerFragment)

Bug: 149670265
Change-Id: Ib37ae0d15f4b89a0ea1d574acb1f081cababa4ae
diff --git a/src/com/android/wallpaper/picker/individual/IndividualPickerFragment.java b/src/com/android/wallpaper/picker/individual/IndividualPickerFragment.java
index c0c4ce5..a05d026 100755
--- a/src/com/android/wallpaper/picker/individual/IndividualPickerFragment.java
+++ b/src/com/android/wallpaper/picker/individual/IndividualPickerFragment.java
@@ -927,8 +927,7 @@
                             }
                         });
             } else { // MOBILE
-                return new PreviewIndividualHolder(
-                        (IndividualPickerActivity) getActivity(), mTileSizePx.y, view);
+                return new PreviewIndividualHolder(getActivity(), mTileSizePx.y, view);
             }
         }