Clean up enclosingCompositingAncestor vs enclosingCompositingAncestorForPaintInvalidation.

Rename enclosingCompositingAncestor to enclosingLayerWithCompositedLayerMapping,
to make clear what it does and distinguish from enclosingCompositingLayerForPaintInvalidation.

Rename enclosingCompositingLayerForPaintInvalidation to enclosingLayerForPaintInvalidation,
since calling it compositing is confusing in the context of the somewhat
complicated ways that layers paint into each other these days.

Remove default argument for enclosingLayerWithCompositedLayerMapping and force
callers to specify for clarity.
Remove the argument to enclosingLayerForPaintInvalidation since no one uses it.

Change one call site in RenderLayerScrollableArea from enclosingLayerWithCompositedLayerMapping to enclosingLayerForPaintInvalidation since it is a paint container.

BUG=384520

Review URL: https://codereview.chromium.org/360063002

git-svn-id: svn://svn.chromium.org/blink/trunk@177270 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Do not include FastMalloc.h in config.h as we no longer redefine new and delete in FastMalloc.h. 

FastMalloc.h use to include cstddef; this header is still needed globally in blink so now it needs to be included explicitly in config.h (and remove the inclusion of it everywhere else in blink).

Not including wtf/WTFExport.h in config.h (indirectly) revealed a bug in NullPtr.h. NullPtr.h now only includes wtf/WTFExport.h conditionally (so that if the compiler supports nullptr does not need to include it).

Review URL: https://codereview.chromium.org/361823004

git-svn-id: svn://svn.chromium.org/blink/trunk@177271 bbb929c8-8fbe-4397-9dbb-9b2b20218538