Google has been working on Native Client for years and it's got years more work if it wants it to become a widely used web technology. One step in that direction is the new support for ARM processors that comes with the new Native Client SDK, version 25, i.e. targeted at Chrome 25, currently in beta.
Native Client, or NaCl for short, is a technology that enables developers to package their C/C++ code and applications into a Native Client app that can be deployed online and which runs in Chrome no matter the platform.
A NaCl app in the Web Store should run on Windows, Mac, Linux and Chrome OS, to the app they'll all look the same. Until now though, there was a big caveat, it only worked on x86 processors, 32-bit or 64-bit.
This wasn't a problem since all the desktop and laptop processors are based on the x86 instruction set, with one big exception, the new cheap Samsung Chromebook that has been so popular in recent months which sports an ARM processor. And, of course, all smartphones and tablets run ARM processors as well.