estimateStrategy() function is called to get the total value of the strategy as well as the individual values of each underlying asset. It does this by looking up all the underlying assets in the strategy and calling
estimateItem() passing the token balance held by the strategy.
estimateItem() function takes a token address and a token amount and estimates the value of that amount in WETH. It does this by querying the
TokenRegistry contract for the address of the
Estimator contract that is used to estimate that particular token. It then calls the estimator's
estimateItem() function and returns the response.