To my knowledge, in Google Chrome there’s not yet a straight way to call an external download managers like IDM, FlashGot, etc for downloading files.
For downloading large files, generally people depend on external download managers, because they offer comparatively faster downloading speed and resume function.
Here is a simple solution to make a direct calls to an external download managers (such as IDM, FlashGot, Free download manager, etc) in Google Chrome.
The extension called oGet provides the option to select the default download manager for Google Chrome for downloading files. Select the highlighted one [see screenshot below] from the list and save the settings.