Revert of TextRun::length() should return an unsigned

Source/platform/fonts/WidthCache.h

 /*
  * Copyright (C) 2012 Apple 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 112 matching lines @@
 
 public:
     WidthCache()
         : m_interval(s_maxInterval)
         , m_countdown(m_interval)
     {
     }
 
     WidthCacheEntry* add(const TextRun& run, WidthCacheEntry entry)
     {
-        if (run.length() > SmallStringKey::capacity())
+        if (static_cast<unsigned>(run.length()) > SmallStringKey::capacity())
             return 0;
 
         if (m_countdown > 0) {
             --m_countdown;
             return 0;
         }
 
         return addSlowCase(run, entry);
     }
 
     void clear()
     {
         m_singleCharMap.clear();
         m_map.clear();
     }
 
 private:
     WidthCacheEntry* addSlowCase(const TextRun& run, WidthCacheEntry entry)
     {
-        unsigned length = run.length();
+        int length = run.length();
         bool isNewEntry;
         WidthCacheEntry *value;
         if (length == 1) {
             SingleCharMap::AddResult addResult = m_singleCharMap.add(run[0], entry);
             isNewEntry = addResult.isNewEntry;
             value = &addResult.storedValue->value;
         } else {
             SmallStringKey smallStringKey;
             if (run.is8Bit())
                 smallStringKey = SmallStringKey(run.characters8(), length);
@@ skipping 40 matching lines @@
 inline bool operator==(const WidthCache::SmallStringKey& a, const WidthCache::SmallStringKey& b)
 {
     if (a.length() != b.length())
         return false;
     return WTF::equal(a.characters(), b.characters(), a.length());
 }
 
 } // namespace blink
 
 #endif // WidthCache_h