enable shared lib support in linux for lua

src/utils/SkLua.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkLua.h"
 #include "SkCanvas.h"
 #include "SkData.h"
@@ skipping 931 matching lines @@
 void SkLua::Load(lua_State* L) {
     register_Sk(L);
     REG_CLASS(L, SkCanvas);
     REG_CLASS(L, SkDocument);
     REG_CLASS(L, SkImage);
     REG_CLASS(L, SkPath);
     REG_CLASS(L, SkPaint);
     REG_CLASS(L, SkRRect);
     REG_CLASS(L, SkTypeface);
 }
+
+extern "C" int luaopen_skia(lua_State* L) {
+    SkLua::Load(L);
+    return 0;
+}