Add smart pointer to Skia

The first attached patch adds a smart pointer template to Skia. The second attached patch refactors SkPaint to use this new SkRefPtr template.

[andrei, 2010-01-07 23:42:56]

I propose adding a smart pointer template to Skia and would appreciate your
feedback.

Thank you,
Andrei

[andrei, 2010-01-15 00:43:00]

Even if the SkRefPtr template is not used internally within Skia, I believe it
would still be useful to clients of Skia.

[agl, 2010-01-15 09:46:35]

deferring to reed on this one.

[duzy, 2010-04-16 08:31:03]

I would give a score to smart pointer like this SkRefPtr.

But the SkRefPtr should need some improvement, I think.

http://codereview.appspot.com/183150/diff/1/2
File include/core/SkRefCnt.h (right):

http://codereview.appspot.com/183150/diff/1/2#newcode174
include/core/SkRefCnt.h:174: T* operator->() const { return fObj; }
operator*() and operator->() would expose 'ref()' and 'unref()' from SkRefCnt to
users, this is bad I think, just take look at this segment:

    SkRefPtr<SkTypeface> typeface;
    ...
    ...
    typeface->unref(); // possible, and really bad
    ...