: the end point of canvas arc is incorrect

Steps to reproduce:

Canvas spec defines start point and end point of arc as follows:

http://www.w3.org/TR/2dcontext2/#dom-context-2d-arc
The points at startAngle and endAngle along this circle's circumference, measured in radians clockwise from the ellipse's semi-major axis, are the start and end points respectively


Actual results:

When endAngle-startAngle is greater than 2π, the end point is the same to the start point regardless of the end angle.


Expected results:

End point of arc must be consistent with end angle

Blink had the same issue and fixed in https://codereview.chromium.org/18286007/

There is a discussion about it in W3C bugzilla: https://www.w3.org/Bugs/Public/show_bug.cgi?id=23050