Use tighter typing for RenderTextFragment::firstLetter()

Source/core/inspector/InspectorCSSAgent.cpp

 /*
  * Copyright (C) 2010, 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:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 762 matching lines @@
         }
     }
 
     HashCountedSet<String> fontStats;
     for (size_t i = 0; i < textNodes.size(); ++i) {
         RenderText* renderer = toRenderText(textNodes[i]->renderer());
         collectPlatformFontsForRenderer(renderer, &fontStats);
         if (renderer->isTextFragment()) {
             RenderTextFragment* textFragment = toRenderTextFragment(renderer);
             if (textFragment->firstLetter()) {
-                RenderObject* firstLetter = textFragment->firstLetter();
+                RenderBoxModelObject* firstLetter = textFragment->firstLetter();
                 for (RenderObject* current = firstLetter->slowFirstChild(); current; current = current->nextSibling()) {
                     if (current->isText())
                         collectPlatformFontsForRenderer(toRenderText(current), &fontStats);
                 }
             }
         }
     }
 
     platformFonts = TypeBuilder::Array<TypeBuilder::CSS::PlatformFontUsage>::create();
     for (HashCountedSet<String>::iterator it = fontStats.begin(), end = fontStats.end(); it != end; ++it) {
@@ skipping 593 matching lines @@
             documentsToChange.add(element->ownerDocument());
     }
 
     m_nodeIdToForcedPseudoState.clear();
     for (HashSet<Document*>::iterator it = documentsToChange.begin(), end = documentsToChange.end(); it != end; ++it)
         (*it)->setNeedsStyleRecalc(SubtreeStyleChange);
 }
 
 } // namespace WebCore