Allow optimization hints to be marked as experimental.

Experimental hints are tagged (in the Optimization proto) with an
experiment name. Experimental hints are not enabled unless an
experiment with a matching name is enabled. Experiments are enabled by
turning on the new base::Feature called kOptimizationHintsExperiments,
with the name of the experiment in a parameter called experiment_name.

Bug: 831817
Change-Id: I6141c70f8f3a8f9adb2c9772b747ee2a0c59b227
Reviewed-on: https://chromium-review.googlesource.com/1132491
Commit-Queue: Jeremy Elson <[email protected]>
Reviewed-by: Ryan Sturm <[email protected]>
Cr-Commit-Position: refs/heads/master@{#574380}
5 files changed