Fixes Mage.Cookies poor performance

[wujashek]

While reviewing performance of Magento 1 and Magento 2 websites I was surprised by the time of Mage.Cookies.get calls execution being around 5-10 ms based on number of cookies stored.

This is how it looks on Land Rover website:

What I've found is that the Cookies class uses document.cookie property in extremely not effective way.

Document.cookie call is not just a string property retrieving -
Quote from w3c documentation on document.cookie

The document.cookie property looks like a normal text string. But it is not.

Single call can take from 0,03 to 10 milliseconds on various browsers/devices.

Simple test to reproduce in different browsers/devices : https://jsfiddle.net/rtxee657/1/.

Description

This pull request reduce the time for a Mage.Cookies.get call around 10 times without any side effects, and that gives average Magento 2 based website 1-2% faster page load.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-cicd2]

All committers have signed the CLA.

[magento-team]

@wujashek thank you for your contribution. Your Pull Request has been successfully merged