UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/47.0.2526.106 Safari/537.36

Steps to reproduce the problem:
Create and load an extension that run following code:

chrome.runtime.getPlatformInfo(function(info) {
  console.log(info.arch);
});

Alternatively, inspect the background page of any existing extension, and run this code from there.

What is the expected behavior?
When Chromium was compiled for, and is running on, 64-bit ARM (also known as aarch64 and armv8), the "arch" field reported by runtime.getPlatformInfo() should indicate that it is a 64-bit architecture.

https://packages.debian.org/stretch/chromium

What went wrong?
I don't have an armv8 machine to test with myself, but the documentation [1] and source code [2] indicates that there is no distinction between 32-bit and 64-bit ARM.

In my particular case this is a problem, because based on this information I'm offering the user a link to download a native messaging host for their platform.

[1]: https://developer.chrome.com/extensions/runtime#type-PlatformArch
[2]: https://cs.chromium.org/chromium/src/chrome/browser/extensions/api/runtime/chrome_runtime_api_delegate.cc?l=289

WebStore page: 

Did this work before? N/A 

Chrome version: 57.0.2987.133  Channel: stable
OS Version: 
Flash Version: Shockwave Flash 22.0 r0