add explicit cast from SkScalar to double

add explicit cast from SkScalar to double

Otherwise the error could happen when SkScalar is SkFixed.

BUG=
TEST=

[guanqun, 2012-02-09 06:55:01]

Please review. Thanks!

BTW: In some skia code, I've seen the assumption that SkScalar is float, is this
assumption valid? Is there any place we still use SkFixed as SkScalar?

[reed1, 2012-02-15 21:43:58]

lgtm

We still support a compile-time flag that makes SkScalar==SkFixed. This is not
exercised by any (known) large clients, as android and chrome always build using
floats, but our internal tests and bots exercise both versions.

[guanqun, 2012-02-16 05:58:20]

On 2012/02/15 21:43:58, reed1 wrote:
> We still support a compile-time flag that makes SkScalar==SkFixed. This is not
> exercised by any (known) large clients, as android and chrome always build
using
> floats, but our internal tests and bots exercise both versions.

Thanks for your info.

And please help land this patch.

[reed1, 2012-02-16 13:20:29]

landed in rev. 3206