In some tests we record how much memory is currently used, say in graphics_WebGLAquarium.py

keyvals = self.GSC.get_memory_keyvals()

Now often it is better to get relative usage since the test started running and the GSC got created:

    def initialize(self):
        self.GSC = graphics_utils.GraphicsStateChecker()

So, track this initial memory usage and add a function get_memory_difference_keyvals() to obtain the delta. Going from there we should replace our memory measurements with relative changes and send these to the Chrome performance dashboard.
https://chromeperf.appspot.com/report?sid=55da93698c24c7b7b0e450638e6c604c6dd6083716a2f04b5be9f49344194d17

I am still thinking if we should just overwrite the old values on the dashboard or if we should create a new set.