Wallpaper preview parallax matches the actual wallpaper's.

Cherry picking the following changes from ub-launcher3-master:
Change-Id: I41c5bbbfdabfeb4e20d77e9b5804842a03211edf
Change-Id: I69afa3f8cc59c77e9c4c25e29e8db8c4beb87462
Change-Id: I82b7ba506d51ee4b3812af5fbdf95d3303b37aef
Change-Id: Id7c2b5483c5535d59be2f8a459ce7788e3c8318a

Bug: 23568800
Change-Id: I343169b9fdc5ceaab3d4b39044627d78b7267868
diff --git a/src/com/android/launcher3/Launcher.java b/src/com/android/launcher3/Launcher.java
index c017dc0..e687ee2 100644
--- a/src/com/android/launcher3/Launcher.java
+++ b/src/com/android/launcher3/Launcher.java
@@ -2757,7 +2757,10 @@
      */
     protected void onClickWallpaperPicker(View v) {
         if (LOGD) Log.d(TAG, "onClickWallpaperPicker");
-        startActivityForResult(new Intent(Intent.ACTION_SET_WALLPAPER).setPackage(getPackageName()),
+        int pageScroll = mWorkspace.getScrollForPage(mWorkspace.getPageNearestToCenterOfScreen());
+        float offset = mWorkspace.mWallpaperOffset.wallpaperOffsetForScroll(pageScroll);
+        startActivityForResult(new Intent(Intent.ACTION_SET_WALLPAPER).setPackage(getPackageName())
+                        .putExtra(WallpaperPickerActivity.EXTRA_WALLPAPER_OFFSET, offset),
                 REQUEST_PICK_WALLPAPER);
 
         if (mLauncherCallbacks != null) {