Clean up SVGResources
Clean up SVGResources

Clean up SVGResources by:
- using nullptr everywhere
- replacing unneeded if checks with ASSERTs
- making ensureResources return a reference to
  indicate it always returns an object, not
  a null pointer

Review URL: https://codereview.chromium.org/724453002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@187327 bbb929c8-8fbe-4397-9dbb-9b2b20218538

modulexcite/blink,modulexcite/blink,nwjs/blink,Bysmyyr/blink-crosswalk,jtg-gg/blink,Pluto-tv/blink-crosswalk,modulexcite/blink,PeterWangIntel/blink-crosswalk,Pluto-tv/blink-crosswalk,smishenk/blink-crosswalk,jtg-gg/blink,smishenk/blink-crosswalk,Pluto-tv/blink-crosswalk,XiaosongWei/blink-crosswalk,XiaosongWei/blink-crosswalk,smishenk/blink-crosswalk,XiaosongWei/blink-crosswalk,nwjs/blink,kurli/blink-crosswalk,kurli/blink-crosswalk,smishenk/blink-crosswalk,PeterWangIntel/blink-crosswalk,kurli/blink-crosswalk,jtg-gg/blink,XiaosongWei/blink-crosswalk,PeterWangIntel/blink-crosswalk,smishenk/blink-crosswalk,kurli/blink-crosswalk,XiaosongWei/blink-crosswalk,nwjs/blink,modulexcite/blink,jtg-gg/blink,jtg-gg/blink,Bysmyyr/blink-crosswalk,PeterWangIntel/blink-crosswalk,kurli/blink-crosswalk,kurli/blink-crosswalk,Pluto-tv/blink-crosswalk,PeterWangIntel/blink-crosswalk,kurli/blink-crosswalk,Bysmyyr/blink-crosswalk,nwjs/blink,Bysmyyr/blink-crosswalk,jtg-gg/blink,Bysmyyr/blink-crosswalk,nwjs/blink,smishenk/blink-crosswalk,Pluto-tv/blink-crosswalk,XiaosongWei/blink-crosswalk,modulexcite/blink,kurli/blink-crosswalk,Pluto-tv/blink-crosswalk,PeterWangIntel/blink-crosswalk,Bysmyyr/blink-crosswalk,XiaosongWei/blink-crosswalk,smishenk/blink-crosswalk,Bysmyyr/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,XiaosongWei/blink-crosswalk,kurli/blink-crosswalk,smishenk/blink-crosswalk,Bysmyyr/blink-crosswalk,modulexcite/blink,jtg-gg/blink,nwjs/blink,smishenk/blink-crosswalk,PeterWangIntel/blink-crosswalk,modulexcite/blink,modulexcite/blink,modulexcite/blink,smishenk/blink-crosswalk,PeterWangIntel/blink-crosswalk,XiaosongWei/blink-crosswalk,jtg-gg/blink,Pluto-tv/blink-crosswalk,nwjs/blink,nwjs/blink,nwjs/blink,kurli/blink-crosswalk,modulexcite/blink,PeterWangIntel/blink-crosswalk,XiaosongWei/blink-crosswalk,nwjs/blink,Bysmyyr/blink-crosswalk,Pluto-tv/blink-crosswalk,jtg-gg/blink,Bysmyyr/blink-crosswalk,PeterWangIntel/blink-crosswalk,jtg-gg/blink