I'm not sure how this is supposed to work in the mobile device (Android / Chrome OS) scenario.
These devices are typically on (but suspended) when they're lost. If this means the master key is still in memory, then the attacker has it.
If, on the other hand, the master key is wiped when the device suspends and is reloaded when you unlock the device, how does your SMS application write your messages (that come in while the device is suspended) to disk? How does the phone lookup your contacts to display the incoming caller name if the device was suspended when the call came in?
You can wipe the master key when you suspend. However it will just mean that there needs to be some unencrypted storage to write down things like incoming text messages. Caller ID will also not work (or be stored in the unencrypted storage).
There are ways to do it, but you will lose security/convenience. It all depend on your threat model and how inconvenient you're willing to make your phone.
These devices are typically on (but suspended) when they're lost. If this means the master key is still in memory, then the attacker has it.
If, on the other hand, the master key is wiped when the device suspends and is reloaded when you unlock the device, how does your SMS application write your messages (that come in while the device is suspended) to disk? How does the phone lookup your contacts to display the incoming caller name if the device was suspended when the call came in?