force readbuffer clients to use specialized readFoo for flattenables

BUG=
R=mtklein@google.com

Review URL: https://codereview.chromium.org/26702002

git-svn-id: http://skia.googlecode.com/svn/trunk/src@11803 2bbb7eff-a529-9590-31e7-b0007b416f81
19 files changed