TFSA only shelter investment or interest gains on money or investments inside the TFSA. So, there's no problem transferring adsense earnings into a TFSA but you'd still need to pay taxes on your earnings prior to the transfer.
For example, let's say you have earned $5000 with adsense. You transfer all $5000 into your TFSA. In the course of the year, you make an additional $500 because you lucked out in your investments. So, what's the situation at the end of the year? You pay tax on your $5000 earnings. Your $500 gain in your TFSA is tax-sheltered.