Merge pull request #1 from alxhub/master

Add a const constructor to Profiler, so it can be used as a no-op implementation.
Release 0.0.6
Added counters
Refactored Counters into a separate class
Merge pull request #2 from google/counters

Added counters
Release 0.0.7
Allowing dynamic extraData and timer id
Release 0.0.8
Basic window.console based implementation