In a landmark decision which marks a sweeping victory for the Vineyard and deals a crippling defeat to the Herring Creek Farm Trust, the chief justice of the Massachusetts Land Court upheld three-acre zoning in the town of Edgartown yesterday. The decision is believed to be the most important legal opinion for the Vineyard since the state Supreme Judicial Court ruled in favor of the Martha's Vineyard Commission on the Island Properties case nearly two decades ago.