Put SVGResourceContainer subtypes into their own property trees.

third_party/WebKit/LayoutTests/platform/linux/paint/invalidation/svg/text-mask-update-expected.txt

 {
   "layers": [
     {
       "name": "LayoutView #document",
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "paintInvalidations": [
         {
           "object": "LayoutSVGRect rect",
           "rect": [10, 3, 46, 22],
           "reason": "style change"
         },
         {
-          "object": "LayoutSVGText text id='text1'",
-          "rect": [10, 3, 46, 22],
-          "reason": "style change"
-        },
-        {
           "object": "LayoutSVGInlineText #text",
           "rect": [10, 33, 43, 22],
           "reason": "layoutObject removal"
         },
         {
-          "object": "LayoutSVGText text id='text2'",
-          "rect": [10, 33, 43, 22],
-          "reason": "full"
-        },
-        {
           "object": "LayoutSVGRect rect",
           "rect": [10, 33, 43, 17],
           "reason": "full"
         }
       ]
     }
   ],
   "objectPaintInvalidations": [
     {
       "object": "LayoutSVGInlineText #text",
@@ skipping 23 matching lines @@
       "object": "LayoutSVGRect rect",
       "reason": "style change"
     },
     {
       "object": "LayoutSVGRect rect",
       "reason": "full"
     }
   ]
 }