Taking an educated guess with grep is indeed the easiest path sometimes.
load_components loads modules and adds them as base class (kinda like use base does).
load_components('Core') loads DBIx::Class::Core and makes DBIx::Class::Core a base class of your class.
DBIx::Class::Core similarly uses load_components loads a number of modules (including DBIx::Class::ResultSourceProxy::Table) and adds them to its list of base classes.
package Result::Item;
use strict;
use warnings;
use base 'DBIx::Class';
__PACKAGE__->load_components( "InflateColumn::DateTime", "Core" );
print "Parents of Result::Item:\n";
print "$_\n" for @Result::Item::ISA;
print "\n";
print "Parents of DBIx::Class::Core:\n";
print "$_\n" for @DBIx::Class::Core::ISA;
Parents of Result::Item:
DBIx::Class::InflateColumn::DateTime
DBIx::Class::Core
DBIx::Class
Parents of DBIx::Class::Core:
DBIx::Class::Relationship
DBIx::Class::InflateColumn
DBIx::Class::PK::Auto
DBIx::Class::PK
DBIx::Class::Row
DBIx::Class::ResultSourceProxy::Table
DBIx::Class