Google is adding something called Emergency Location Service to Android. It will be rolling out through Google Play Services (which automatically updates in the background, so you don't have to do anything to get it). With the huge reach that Play Services has, this means that theoretically Emergency Location Service is supported by 99% of Android devices out there.
However, this can't just be turned on by Google - the company first has to talk to mobile network operators and emergency infrastructure providers in each country in order to enable support. So the worldwide rollout is sure to take some time. For now, the new feature is available in the UK and Estonia, through partnerships Google's forged with the carriers and emergency services listed in the picture below.
Here's how it works. When you place an emergency call from your Android device (and if you're on a supported carrier in a supported country), your location will automatically be sent to the emergency services. The information goes straight from your phone to the emergency operator, bypassing Google entirely. Obviously this uses the same location tech available to apps on your phone, and so Wi-Fi, GPS, and cell towers can all be involved in order to produce a reliable location both indoors and outdoors.