create outer forloop to support loops=-1
create outer forloop to support loops=-1

Change-Id: I1f76a798f3f95afb82ab739ab5343bf52b233c7d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/226079
Reviewed-by: Mike Reed <f5cabf8735907151a446812c9875d6c0c712d847@google.com>
Commit-Queue: Mike Reed <f5cabf8735907151a446812c9875d6c0c712d847@google.com>
Auto-Submit: Mike Reed <f5cabf8735907151a446812c9875d6c0c712d847@google.com>

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