Use F12 to open Developer Tools on Chrome
Open Keyboard Shortcuts Preferences
Click "Mission Control" from the list
Untick "Show Dashboard" (disable default beahviour of F12)
Click "Application Shortcuts" from the list
Click the "+" below the right-hand list
Select Google Chrome from the drop down list
In "Menu Title", type Developer Tools
Click in "Keyboard Shortcut", then press F12