Optionally use new scheme for optimization configs.
Optionally use new scheme for optimization configs.

The GN optimization config setup is being moved. This patch allows blink to switch between the new and old ones.

Review URL: https://codereview.chromium.org/1330693002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@201835 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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