As documented here, Google Chrome has an automatic spell-check built in, and it is possible to disable it for certain fields temporarily.
Can it be disabled for all sites?
Go to Chrome Settings (Enter
chrome://settings/ in address bar)
Click on Advance Settings and then click on
Language and Input settings and then untick the
Enable spell checking check box.
chrome://settings/languages in the address bar
A dialogue box will open listing the installed languages.
At the bottom is a tickbox labelled
Enable Spell Checking.
Untick the box. This should disable spell checking everywhere.