code: public String getTexCoordShaderVar(String texName)
      {
          GVRTexture tex = textures.get(texName);
          if (tex != null)
          {
              return tex.getTexCoordShaderVar();
          }
          return null;
      }
docs: Gets the name of the shader variable to get the texture
  coordinates for the named texture.
  
  @param texName name of texture
  @return name of shader variable