By Douglas Busvine MOSCOW, March 7 (Reuters) - Russia on Thursday filed fraud charges against William Browder, head of London-based investment fund Hermitage Capital Management, over dealings a decade ago in shares in state gas firm Gazprom. The charges were filed before Browder was due to be tried on Monday in absentia, along with Hermitage's dead lawyer Sergei Magnitsky, in a separate tax evasion case that has stoked tensions between Moscow and the West.