Move the SVG container code from rendering/svg to layout/svg.

LayoutTests/svg/custom/absolute-root-position-masking-expected.txt

Index: LayoutTests/svg/custom/absolute-root-position-masking-expected.txt
diff --git a/LayoutTests/svg/custom/absolute-root-position-masking-expected.txt b/LayoutTests/svg/custom/absolute-root-position-masking-expected.txt
index 97efbb6378ec9c3bd75c80d7f5e9cc33a71f01ed..50a82605096098de13b058b19c6c8541ed04ee2c 100644
--- a/LayoutTests/svg/custom/absolute-root-position-masking-expected.txt
+++ b/LayoutTests/svg/custom/absolute-root-position-masking-expected.txt
@@ -7,7 +7,7 @@ layer at (0,100) size 300x300
   RenderSVGRoot {svg:svg} at (200,300) size 100x100
     LayoutSVGEllipse {svg:circle} at (200,300) size 100x100 [fill={[type=SOLID] [color=#0000FF]}] [cx=300.00] [cy=300.00] [r=100.00]
       [masker="mask"] LayoutSVGResourceMasker {svg:mask} at (180,180) size 420x420
-    RenderSVGHiddenContainer {svg:defs} at (0,0) size 0x0
+    LayoutSVGHiddenContainer {svg:defs} at (0,0) size 0x0
       LayoutSVGResourcePattern {svg:pattern} [id="pattern"] [patternUnits=objectBoundingBox] [patternContentUnits=userSpaceOnUse]
         LayoutSVGRect {svg:rect} at (0,100) size 300x300 [fill={[type=SOLID] [color=#FFFFFF]}] [x=0.00] [y=0.00] [width=600.00] [height=600.00]
       LayoutSVGResourceMasker {svg:mask} [id="mask"] [maskUnits=objectBoundingBox] [maskContentUnits=userSpaceOnUse]