This fixes a number of things that are warnings in the Mac compiler....

base/cross/bits.h

 /*
  * Copyright 2009, 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.
@@ skipping 37 matching lines @@
   int log = 0;
   unsigned int value = n;
   for (int i = 4; i >= 0; --i) {
     int shift = (1 << i);
     unsigned int x = value >> shift;
     if (x != 0) {
       value = x;
       log += shift;
     }
   }
-  DCHECK_EQ(value, 1);
+  DCHECK_EQ(value, 1u);
   return log;
 }
 
 // Returns the integer i such as 2^(i-1) < n <= 2^i
 static inline int Log2Ceiling(unsigned int n) {
   if (n == 0) {
     return -1;
   } else {
     // Log2Floor returns -1 for 0, so the following works correctly for n=1.
     return 1 + Log2Floor(n - 1);
   }
 }
 
 }  // namespace bits
 }  // namespace base
 }  // namespace o3d
 
 #endif  // O3D_BASE_CROSS_BITS_H_