Add dummy mips stub to make Blink compile on MIPS again.

We should implement the actual stub when we can get it tested.
Right now this code just sits there and is not used in the shipping
system and therefore the dummy stub is safe for now.

R=erik.corry@gmail.com, vegorov@chromium.org
BUG=

Review URL: https://codereview.chromium.org/112053009

git-svn-id: svn://svn.chromium.org/blink/trunk@164074 bbb929c8-8fbe-4397-9dbb-9b2b20218538