Use tighter typing in table rendering code

Source/core/rendering/FastTextAutosizer.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 394 matching lines @@
 
     Cluster* cluster = currentCluster();
     if (cluster->m_root != table)
         return;
 
     // Pre-inflate cells that have enough text so that their inflated preferred widths will be used
     // for column sizing.
     for (RenderObject* section = table->firstChild(); section; section = section->nextSibling()) {
         if (!section->isTableSection())
             continue;
-        for (RenderObject* row = toRenderTableSection(section)->firstChild(); row; row = row->nextSibling()) {
-            if (!row->isTableRow())
-                continue;
-            for (RenderObject* cell = toRenderTableRow(row)->firstChild(); cell; cell = cell->nextSibling()) {
-                if (!cell->isTableCell() || !cell->needsLayout())
+        for (RenderTableRow* row = toRenderTableSection(section)->firstRow(); row; row = row->nextRow()) {
+            for (RenderTableCell* cell = row->firstCell(); cell; cell = cell->nextCell()) {
+                if (!cell->needsLayout())
                     continue;
-                RenderTableCell* renderTableCell = toRenderTableCell(cell);
-                beginLayout(renderTableCell);
-                inflate(renderTableCell);
-                endLayout(renderTableCell);
+                beginLayout(cell);
+                inflate(cell);
+                endLayout(cell);
             }
         }
     }
 }
 
 void FastTextAutosizer::endLayout(RenderBlock* block)
 {
     ASSERT(shouldHandleLayout());
 
     if (block == m_firstBlockToBeginLayout) {
@@ skipping 678 matching lines @@
 FastTextAutosizer::DeferUpdatePageInfo::~DeferUpdatePageInfo()
 {
     if (FastTextAutosizer* textAutosizer = m_mainFrame->document()->fastTextAutosizer()) {
         ASSERT(textAutosizer->m_updatePageInfoDeferred);
         textAutosizer->m_updatePageInfoDeferred = false;
         textAutosizer->updatePageInfoInAllFrames();
     }
 }
 
 } // namespace WebCore