Measure usage metrics to prepare for adaptive fetching rates in M55

Measure usage metrics to prepare for adaptive fetching rates in M55

In order to scale to 100% of users in M55, we need adaptive fetching
rates for server-side suggestions on the new tab page. This CL
implements reporting of usage metrics to UMA. We need to collect these
metrics already in M54 so that we have enough data to define default
parameters for the adaptive fetching rates in M55.

Design doc: https://docs.google.com/a/google.com/document/d/1tDl2Dx_ZPnSyoe7hAe55mT2uTeXDaFVphqsWZEjp3EQ/edit?usp=sharing

BUG=644716
Review-Url: https://codereview.chromium.org/2315273002
Cr-Commit-Position: refs/heads/master@{#417336}
(cherry picked from commit e13510e5938155d4eb7b8a742919a11aa7f8556c)

Committed: https://chromium.googlesource.com/chromium/src/+/fac6b13156a4d9c89778334eb9013354ddef81ec

[Marc Treib, 2016-09-14 11:12:43]

Description was changed from

==========
Measure usage metrics to prepare for adaptive fetching rates in M55

In order to scale to 100% of users in M55, we need adaptive fetching
rates for server-side suggestions on the new tab page. This CL
implements reporting of usage metrics to UMA. We need to collect these
metrics already in M54 so that we have enough data to define default
parameters for the adaptive fetching rates in M55.

Design doc:
https://docs.google.com/a/google.com/document/d/1tDl2Dx_ZPnSyoe7hAe55mT2uTeXD...

BUG=644716

Review-Url: https://codereview.chromium.org/2315273002
Cr-Commit-Position: refs/heads/master@{#417336}
(cherry picked from commit e13510e5938155d4eb7b8a742919a11aa7f8556c)
==========

to

==========
Measure usage metrics to prepare for adaptive fetching rates in M55

In order to scale to 100% of users in M55, we need adaptive fetching
rates for server-side suggestions on the new tab page. This CL
implements reporting of usage metrics to UMA. We need to collect these
metrics already in M54 so that we have enough data to define default
parameters for the adaptive fetching rates in M55.

Design doc:
https://docs.google.com/a/google.com/document/d/1tDl2Dx_ZPnSyoe7hAe55mT2uTeXD...

BUG=644716

Review-Url: https://codereview.chromium.org/2315273002
Cr-Commit-Position: refs/heads/master@{#417336}
(cherry picked from commit e13510e5938155d4eb7b8a742919a11aa7f8556c)

Committed:
https://chromium.googlesource.com/chromium/src/+/fac6b13156a4d9c89778334eb901...
==========

[Marc Treib, 2016-09-14 11:12:45]

Committed patchset #1 (id:1) manually as
fac6b13156a4d9c89778334eb9013354ddef81ec.