NVIDIA CEO Jen-Hsun Huang said that Portal will come to the Shield handheld system. NVIDIA is doing the work to create a full port of the game with the aid of Valve. At first, Portal will be exclusive to Android devices running on NVIDIA chipsets, but it won't technically be locked to that hardware. This means that you'll not only be able to pirate the APK when it is released (though we would never condone that), but that there is a chance that Portal will see a wider release later on.
There is no word yet on when the game will be coming to Android. The only word used was "soon", which doesn't really mean much. There was also no word on pricing for the game. If all goes well, NVIDIA hopes to port more PC games to the Android platform.
source: The Verge