Change metric name format for NavigationTiming events

This patch changes the name format of NavigationTiming metrics logged to
Graphite to better match how we analyze the data. The change allows us to
include data from all countries, not just the top 10.

Change-Id: I93403c81a71d3935f5e6fce93eee9f21d86fe3bb
Merge "Change metric name format for NavigationTiming events" into production