message: Fix compilation warnings for ggp platform.
  This fix the warning about comparison of integers of different signs.
diff: @@ -47,11 +47,11 @@ public:
  void Set(uint64_t *calls, size_t num)
  {
  numLevels = num;
  - for(int i = 0; i < numLevels; i++)
  + for(size_t i = 0; i < numLevels; i++)
  addrs[i] = calls[i];
  }
  - size_t NumLevels() const { return size_t(numLevels); }
  + size_t NumLevels() const { return numLevels; }
  const uint64_t *GetAddrs() const { return addrs; }
  private:
  GgpCallstack(const Callstack::Stackwalk &other);
  @@ -71,12 +71,12 @@ private:
  numLevels--;
  }
  - for(int i = 0; i < numLevels; i++)
  + for(size_t i = 0; i < numLevels; i++)
  addrs[i] = (uint64_t)addrs_ptr[i + offs];
  }
  uint64_t addrs[128];
  - int numLevels;
  + size_t numLevels;
  };
  namespace Callstack
  