Remove uses of SkBitmap::Config (deprecated) from core/ and platform/.

      These should be replaced by SkColorType and SkImageInfo.
In many cases, shortcut methods like SkBitmap::allocN32Pixels can be used.

BUG=

Review URL: https://codereview.chromium.org/201213002

git-svn-id: svn://svn.chromium.org/blink/trunk@169464 bbb929c8-8fbe-4397-9dbb-9b2b20218538