If an Android device (phone or tablet) has ever logged on to a particular Wi-Fi network, then Google probably knows the Wi-Fi password. Considering how many Android devices there are, it is likely that Google can access most Wi-Fi passwords worldwide.
Recently IDC reported that 187 million Android phones were shipped in the second quarter of this year. That multiplies out to 748 million phones in 2013, a figure that does not include Android tablets.
Many (probably most) of these Android phones and tablets are phoning home to Google, backing up Wi-Fi passwords along with other assorted settings. And, although they have never said so directly, it is obvious that Google can read the passwords.Source