Request: Add mixin for #sizedImgDiv

[kristfal]

Description

A use case for iron-image can be to add a box shadow inset in order to render a gradient across the image, such as:

-webkit-box-shadow: inset 0px -29px 55px -18px rgba(0,0,0,0.65);
box-shadow: inset 0px -29px 55px -18px rgba(0,0,0,0.65);

Setting this style on iron-image will not render as #sizedImgDiv is rendered on top of the iron-image tags.

Expected outcome

Should be able to use box-shadow insets with iron-image

Actual outcome

Box shadow insets is not rendering because they need to be applied to #sizedImgDiv

Proposed solution

Add a mixin to #sizedImgDiv

Let me know if you want a PR.

Browsers Affected

• [x] Chrome
• [x] Firefox
• [x] Safari 9
• [x] Safari 8
• [x] Safari 7
• [x] Edge
• [x] IE 11
• [x] IE 10

[bicknellr]

If you'd like to submit a PR, feel free; this doesn't seem contentious or breaking.

[kristfal]

@bicknellr See #83. Also, tests are failing for Firefox – there seems to be an issue with the CI.

[bicknellr]

Yeah, we've been having some issues with Firefox and the test framework lately. Thanks for the PR. After considering this again, I think this might be outside the scope of iron-image given that img also behaves this way. Here's a demo.