Support unknown Android target devices via environment variables.

This is useful for working with prototypes and uncommon devices.

NOTRY=true
R=djsollen@google.com, scroggo@google.com

Author: halcanary@google.com

Review URL: https://codereview.chromium.org/263673004

git-svn-id: http://skia.googlecode.com/svn/trunk@14495 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed