Add support for new canvas ellipse method.

LayoutTests/fast/canvas/script-tests/js-ellipse-implementation.js

+function rad2deg(x) {
+  return x * 180 / Math.PI;
+}
+
+function ellipseUsingArc(context, x, y, radiusX, radiusY, rotation, startAngle, endAngle, anticlockwise)
+{
+    var transform = new WebKitCSSMatrix();
+    transform = transform.translate(x, y);
+    transform = transform.rotate(rad2deg(rotation));
+    transform = transform.scale(radiusX, radiusY);
+
+    /*
+    Use WebKitCSSMatrix instead of as follows, because using WebKitCSSMatrix computes float values more precisely.
+    It is because we don't want to fail pixel comparison due to float precision.
+      context.translate(x, y);
+      context.rotate(rotation);
+      context.scale(radiusX, radiusY);
+    */
+    context.save();
+    context.transform(transform.a, transform.b, transform.c, transform.d, transform.e, transform.f);
+    context.arc(0, 0, 1, startAngle, endAngle, anticlockwise);
+    context.restore();
+}
+