Chrome has a hidden page that shows the amount of data transferred in your current session and the total amount of data transferred (ever since this feature was added).
Open a new tab, paste this in the address bar and press Enter:
chrome://net-internals/#bandwidth
The stats will look like this:
Use a simple calculation to turn the number (which are in KB) into megabytes (MB):
Number in KB / 1024 = MB
The Savings rows are for Android and iOS versions of Chrome if the data saving is enabled.