Summary:
Set up basic primitives for user interaction tracking. I hope the docs and unit tests in this diff are self explanatory :)
In upcoming diffs:
* Wire up to scuba events
* Annotate all important parts of Flipper Chrome
* Investigate if we can wrap important interactions of ANT by default
Reviewed By: jknoxville
Differential Revision: D25120234
fbshipit-source-id: 9849d565d7be27e498cc2b4db33e7d6e6938ee06
b885ff3b9e