fix the inconsisencies of HTML element with both box-shadow and border-radius

[hybtalented]

Summary

This PR fixes the unexpect rendering of HTML element with box-shadow and border-radius styles. It also improve the performance of box-shadow with inset property.

here is the contract while the issues has been sovled:

origin html without border

render by html2canvas without border

origin html with border

render by html2canvas with border
Closing issues

Fixes #1987
maybeFixed #1856 （I can't assess the jsfiddle, so it not clear whether it was fixed.）

[hybtalented]

Summary

This PR fixes the unexpect rendering of HTML element with box-shadow and border-radius styles. It also improve the performance of box-shadow with inset property.

origin html without border

render by html2canvas without border

origin html with border

render by html2canvas with border

Closing issues

Fixes #1987
maybeFixed #1856 （I can't assess the jsfiddle, so it not clear whether it was fixed.）

It looks like the pictures have been down. The effect of the changes can be test in the test page http://localhost:8080/tests/reftests/background/box-shadow.html

[trollr]

@niklasvh could you please merge this one :) That would be great

[abdurrahmanyildirim]

@niklasvh This solution works well. Could you merge this?

[cyan-2048]

hi i need this, any way to get a copy of a compiled JS file for this fork?

[makidoll]

I'd like this merged too!

[Mamezou-zhang-yong]

I'd like this merged too, would you have any schedule to merge it.

[bastienlemaitre]

@niklasvh ?

[Inviz]

I tried this branch and the shadows still look pretty strangely, but it's better. However the "maybefix" part is not fixed.