Add GYP target for sk_tool_utils.* component.

tools/sk_tool_utils.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef sk_tool_utils_DEFINED
 #define sk_tool_utils_DEFINED
 
-#include "SkCanvas.h"
-#include "SkBitmap.h"
+#include "SkImageInfo.h"
+
+class SkBitmap;
+class SkCanvas;
 
 namespace sk_tool_utils {
 
     const char* colortype_name(SkColorType);
 
     /**
      *  Call canvas->writePixels() by using the pixels from bitmap, but with an info that claims
      *  the pixels are colorType + alphaType
      */
     void write_pixels(SkCanvas*, const SkBitmap&, int x, int y, SkColorType, SkAlphaType);
-}
 
-#endif
+}  // namespace sk_tool_utils
+
+#endif  // sk_tool_utils_DEFINED