be conservative when identifying unique true virtual method overrides
be conservative when identifying unique true virtual method overrides

Summary: This adds another safe-guard when identifying unique true virtual method invocation targets, taking into account that certain interfaces might have additional implementations generated at runtime.

Reviewed By: minjang

Differential Revision: D29698631

fbshipit-source-id: 871831b743dac224149710a048e5c5e030bc452d

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