Convert libyuv to a static library in GN.
Convert libyuv to a static library in GN.

We have discovered that this should increase build performance in some cases.

http://crbug.com/627637

R=fbarchard@google.com

Review URL: https://codereview.chromium.org/2163213005 .

lemenkov/libyuv,lemenkov/libyuv,yarrcc/libyuv-ios,lemenkov/libyuv,lemenkov/libyuv,yarrcc/libyuv-ios,yarrcc/libyuv-ios,yarrcc/libyuv-ios