The problem is that the graphics cache only counts the size of the SVG
text, which is stored in SvgData::maSvgDataArray.  However the
SvgData::maSequence may use a lot more memory, as it may contain
de-compressed bitmaps that are stored as base64-encoded PNGs in the SVG
text.

For example icon-themes/galaxy/brand/flat_logo.svg is 812 Ko but contains
60 Mo of bitmaps.

This may cause excessive memory usage and failure to export documents
due to OOM; according to valgrind massif, the bitmap buffers use 90% of
the heap.

Add a new interface com::sun::star::util::XAccounting, and implement
it in drawinglayer BasePrimitive2D.  VCL SvgData can't access
drawinglayer via C++ directly so this looks like the best approach.

Change-Id: I5a7c3147733e23473c1decabed24c1f79d951c7d
Reviewed-on: https://gerrit.libreoffice.org/30669Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>