Rename CompositingState to CompositingRecursionData

In preparation to make compositing state an explicit concept in the
code, we have to re-name a data structure that is already named
CompositingState. Actually this structure is just the state
that needs to be tracked as part of recursion for the function
RenderLayerBacking::computeCompositingRequirements().

BUG=233466
R=jchaffraix@chromium.org

Review URL: https://codereview.chromium.org/25982003

git-svn-id: svn://svn.chromium.org/blink/trunk@158962 bbb929c8-8fbe-4397-9dbb-9b2b20218538