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TimelineBasedMeasurement lets us compute a variety of different metrics for pages that do complex sequences of interactions. Whereas traditional telemetry measurements focus on reporting a single type of value for many pages, this lets a page decide what types of metrics it emits based on the behaviors its page actually performs.

The contract is that the page emits
console.time/timeEnd calls of a certain format describing when it is doing
something worth noting, and what kind fo interaction it is doing. For instance,
if a drawer animation is runnign, it would emit:
  MeasurementRequest.Drawer/smoothness

This tells the timelineBasedMeasurement that the timeline data generated during this time
should be analyzed for smoothness information, with results benig reported as things like
Drawer.frame_time.

Depends on https://codereview.chromium.org/177093013

BUG=345922
NOTRY=True

Review URL: https://codereview.chromium.org/165673008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255434 0039d316-1c4b-4281-b951-d872f2087c98