add readPtr and writePtr to SkReader32 and SkWriter32
add template helper SkSWriter32, which allocates initial storage buffer
Review URL: https://codereview.appspot.com/6299075

git-svn-id: http://skia.googlecode.com/svn/trunk@4237 2bbb7eff-a529-9590-31e7-b0007b416f81
3 files changed