Allow the minimum time between banner trigger visits to be varied via field trials.
The current heuristics for banner triggering are hard-coded. This CL
allows the minimum time between visits that are counted for the purposes
of banner triggering to be varied via field trials. The time will
default to the current value, which is one visit per day (implemented by
bucketing all visits to local midnight time). The new implementation
will bucket to a given resolution in minutes, where the specified
resolution is less than one day and evenly divisible into the number of
minutes in a day.
BUG=487519
Review URL: https://codereview.chromium.org/
1306693005
Cr-Commit-Position: refs/heads/master@{#345228}