Bug 866254: fix failure to initialize search service in cases where the async initialization fails to complete before the synchronous fallback is invoked, r=Yoric

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extra : transplant_source : z2%D7Os2%89%28%5C9%3Ab%BF%0F%15%F3%10x%7Ff
Bug 866254 followup: improve debug logging and minor cleanup, r=Yoric

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extra : transplant_source : %2BS%06%0A%E05%B4%B7%B9%3F%92%8B%B1%AAB%ADL%3A%BC%1E