Support existence_watermark_deadline for fetching GlobalData. Return empty values in the case that no global data was written and the corresponding watermark has advanced passed the deadline.
Support existence_watermark_deadline for fetching GlobalData. Return empty
values in the case that no global data was written and the corresponding
watermark has advanced passed the deadline.

----Release Notes----

[]
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=90444121

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