Remove CompositingUpdateOnScroll

This CL teaches the callers of CompositingUpdateOnScroll how to do partial
compositing updates. Now that they're smarter, we can use
CompositingUpdateAfterCompositingInputChange and we don't need
CompositingUpdateOnScroll anymore.

Review URL: https://codereview.chromium.org/326443002

git-svn-id: svn://svn.chromium.org/blink/trunk@175729 bbb929c8-8fbe-4397-9dbb-9b2b20218538