Replace RenderArena with PartitionAlloc.

Source/core/page/Page.h

Index: Source/core/page/Page.h
diff --git a/Source/core/page/Page.h b/Source/core/page/Page.h
index 9e140269da3f45a825f7947c555d2de2df7dc48b..9477552ba0433e7922752dbffdd2cdf2c126f9a0 100644
--- a/Source/core/page/Page.h
+++ b/Source/core/page/Page.h
@@ -84,16 +84,6 @@ typedef uint64_t LinkHash;
 
 float deviceScaleFactor(Frame*);
 
-struct ArenaSize {
-    ArenaSize(size_t treeSize, size_t allocated)
-        : treeSize(treeSize)
-        , allocated(allocated)
-    {
-    }
-    size_t treeSize;
-    size_t allocated;
-};
-
 class Page : public Supplementable<Page> {
     WTF_MAKE_NONCOPYABLE(Page);
     friend class Settings;
@@ -118,8 +108,6 @@ public:
     explicit Page(PageClients&);
     ~Page();
 
-    ArenaSize renderTreeSize() const;
-
     void setNeedsRecalcStyleInAllFrames();
 
     RenderTheme* theme() const { return m_theme.get(); }