Set default chrome path based on the os.

Added code for finding the default chrome binary path based on the os running. For Windows, will try the following paths in this order, '%LOCALAPPDATA%\Google\Chrome\Application\chrome.exe', 'C:\Program Files\Google\Chrome\Application\chrome.exe', 'C:\Program Files (x86)\Google\Chrome\Application\chrome.exe'. For OS X, will only try '/Applications/Google Chrome.app/Contents/MacOS/Google Chrome'. For Linux, '/usr/bin/google-chrome' and '/usr/bin/chromium-browser' will be tried.