How to step into a native C++ dll in Visual Studio?

I'm debugging my C# unity code through visual studio, and I would like to step into my native C++ code. From C#, I am loading my native c++ plugin using the LoadLibrary function.

 [ DllImport( "kernel32.dll" ) ]  public static extern IntPtr LoadLibrary( string dllToLoad );

Although my dll loads successfully and I can call functions inside my C++ plugin, I can't step into my C++ code and I can't see my dll in Visual Studio's modules window.

Is Visual Studio not loading my pdb? I've already set the dll's pdb location in Visual Studio Tools-->Options-->Debugging->Symbols

Screenshot of my modules window after calling LoadLibrary() on my dll: http://puu.sh/pFRvc/fa9d73a3db.png