Move file web_links into the meta_a, meta_b headers Web links should be part of the metadata for the two halves of a diff. The protocol uses meta_a and meta_b to represent the halves, with contained fields for specific values. Also avoid unnecessary copying of the WebLinkInfo by reusing the created list from the WebLinks factory. Change-Id: I2c31cad2a4fed11e513f81cd613742534662a663