Add a release procedure to SkMallocPixelRef; remove SkDataPixelRef

Add a release procedure to SkMallocPixelRef; remove SkDataPixelRef

This works in a way that is similar to SkData.

SkMallocPixelRef::NewWithProc

    Motivation: Chrome has a ETC1PixelRef which calls delete[] on the
    pixles on destruction.  There is no reason for them to almost
    duplicate our class, when we can provide them a more flexible
    class.  Example use:

      static void delete_uint8_proc(void* ptr, void*) {
        delete[] static_cast<uint8_t>(ptr);
      }
      SkPixelRef* new_delete_pixref(const SkImageInfo& info,
                                    SkColorTable* ctable) {
        size_t rb = info.minRowBytes();
        return SkMallocPixelRef::NewWithProc(
          info, rb, ctable,
          new uint8_t[info.getSafeSize(rb)],
          delete_uint8_proc, NULL);
      }

SkMallocPixelRef::NewWithData

	Motivation:  This allows up to eliminate SkDataPixelRef.  We
    modified SkImage_Raster to use MallocPixelRef rather than
    SkDataPixlRef.

Also:  Unit tests in tests/MallocPixelRefTest.

BUG=
R=reed@google.com

Committed: https://code.google.com/p/skia/source/detail?r=12861

[hal.canary, 2013-12-30 14:06:47]

ptal; is this worth doing?

[reed1, 2013-12-30 16:18:48]

lgtm

[hal.canary, 2014-01-02 17:29:36]

Committed patchset #4 manually as r12861 (presubmit successful).