Use SkBitmapHeap for shaders in SkGPipe.

Required adding a new feature to SkBitmapHeap, allowing it to defer
adding owners, since sometimes we flatten a shader, but then do not
unflatten it, since we already had a copy in the heap, so the owners
never get removed.

Reviewed at https://codereview.appspot.com/6464053/

Review URL: https://codereview.appspot.com/6465047

git-svn-id: http://skia.googlecode.com/svn/trunk@5082 2bbb7eff-a529-9590-31e7-b0007b416f81
4 files changed