UserAgent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:58.0) Gecko/20100101 Firefox/58.0

Steps to reproduce the problem:
1. Download chromium source
2. gn gen out/Release --args=" mips_use_msa=true target_os=\"android\" target_cpu=\"mips64el\" mips_use_msa=true is_debug=false"
3. ninja -C out/Release system_webview_apk

What is the expected behavior?

What went wrong?
Build fails on libwebp because of unused functions.

Did this work before? N/A 

Chrome version: trunk  Channel: n/a
OS Version: 
Flash Version: n/a

Cherry-picking this solves the problem: crrev.com/c/894366