Rename chromium-android port to android

Also renames the ChromiumAndroidPort class to AndroidPort.

A later change will update the relevant LayoutTest platform directory
accordingly.

BUG=231188
R=ojan@chromium.org

Review URL: https://codereview.chromium.org/18292002

git-svn-id: svn://svn.chromium.org/blink/trunk@153597 bbb929c8-8fbe-4397-9dbb-9b2b20218538