Fix incorrect image magnifier size bug in Safari

[dannynimmo]

Description

This pull request fixes a bug in the product gallery magnifier (zoom). In some cases (e.g. in the Safari browser), the image full size is calculated incorrectly, due to the image not being loaded before the dimensions are checked.

The fix makes use of the image element properties naturalWidth & naturalHeight which can check the full size of the image without needing to re-create it from the src. naturalWidth & naturalHeight are supported in IE9+, and all other browsers.

Fixed Issues (if relevant)

1. Product image zoom (magnifier) is broken in Safari #17416: Product image zoom (magnifier) is broken in Safari

Manual testing preconditions

1. Enable the magnifier in the Luma theme in etc/view.xml
2. Safari browser (v11.1.2)
3. Remote environment (issue does not exist on local environments due to the bug being a race condition from the image loading)

Manual testing scenarios

1. Browse to product detail page with a large image
2. Click the image to open the fullscreen gallery
3. Click on the "zoom in" button

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-engcom-team]

Hi @dannynimmo. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me {$VERSION} instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[magento-engcom-team]

Hi @VladimirZaets, thank you for the review.
ENGCOM-2698 has been created to process this Pull Request

[magento-engcom-team]

@dannynimmo thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[dannynimmo]

Hi @magento-engcom-team, how can I get the Travis CI build to pass? The build failed on the below step:

The command if [ $TEST_SUITE != "functional" ] && [ $TEST_SUITE != "js" ]; then phpunit -c dev/tests/$TEST_SUITE $TEST_FILTER; fi exited with 2.

I don't believe this is related to this pull request.

[magento-engcom-team]

Hi @dannynimmo. Thank you for your contribution.
We will aim to release these changes as part of 2.3.0.
Please check the release notes for final confirmation.