Explicitly friend ::SkPrivateEffectInitializer to flattenables.
Explicitly friend ::SkPrivateEffectInitializer to flattenables.

Looks like the -Wmicrosoft warnings in the bug are coming up specificically
because many the effects in SkLightingImageFilter are defined inside an
anonymous namespace (spanning, I think, lines 33-702 today).

BUG=skia:4091

No public API changes.
TBR=reed@google.com

Review URL: https://codereview.chromium.org/1311783004

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