Breaking the dependency of FilterOperations on core/fetch.

External SVG CSS filters require tracking of loaded resources, which adds
a dependency on core/fetch in platform/graphics/filters. This patch moves
the tracking of DocumentResourceRequests to ReferenceFilterBuilder (the
class that uses them) and modifies other call sites to set and clear them.

R=senorblanco@chromium.org, abarth, senorblanco
BUG=303334

Review URL: https://codereview.chromium.org/59313005

git-svn-id: svn://svn.chromium.org/blink/trunk@161930 bbb929c8-8fbe-4397-9dbb-9b2b20218538