Prevent recomputing of metric metadata in EvolutionMetrics

[caddoo]

Description:

As part of an effort to improve the performance of the all websites dashboard, an optimisation has been done here to prevent recomputing of ratio, currency symbol, period name and previousRange.

Reducing the overall impact the call to Piwik\Plugins\CoreHome\Columns\Metrics\EvolutionMetric::compute has

XHProfs

All Websites Dashboard - Without Change

All Websites Dashboard - With Change

Notice number of calls to compute are the same

Evolution popup

It was suggested to make sure the performance of this popup wasn't affected, but in testing it turns out that that popup doesn't touch EvolutionMetric::compute @mneudert can you confirm?

Review

• Functional review done
• Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• Security review done
• Wording review done
• Code review done
• Tests were added if useful/possible
• Reviewed for breaking changes
• Developer changelog updated if needed
• Documentation added if needed
• Existing documentation updated if needed

[michalkleiner]

LGTM