This is a callback that will be called by the system when a bundle is about to be canceled.  The reason parameter will hold a value indicating the reason the bundle is being canceled. Currently the only implemented reason is HC.BundleCancel.Reason.UserCancel. 

reason: HC.BundleCancel.Reason.UserCancel

userParam: <value of userParam passed into bundleStart()>

Return: HC.BundleCancel.Response.OK OR HC.BundleCancel.Response.Commit

Cancel can be canceled by returning HC.BundleCancel.Response.Commit in which case the bundle will be commited instead of canceled.

Note: bundling is an experimental feature and may be deprecated