Issue 137818: Large canvas does not honor containing div’s border-radius
I solved this with CSS tag to parent div to:
transform: translate3d(0,0,0);
it works on the current chrome version 36.0.1985.143 m
#box {
width: 150px;
height: 150px;
background-color: blue;
border-radius: 50px;
overflow: hidden;
transform: translate3d(0,0,0);
}