Add test for platform encoders, turn off platform encoders by default

src/ports/SkImageEncoder_CG.cpp

 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkTypes.h"
 #if defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS)
 
@@ skipping 108 matching lines @@
         return false;
     }
     SkAutoTCallVProc<CGImage, CGImageRelease> agimage(image);
 
     CGImageDestinationAddImage(dst, image, nullptr);
     return CGImageDestinationFinalize(dst);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
+#ifdef SK_USE_CG_ENCODER
 static SkImageEncoder* sk_imageencoder_cg_factory(SkImageEncoder::Type t) {
     switch (t) {
         case SkImageEncoder::kICO_Type:
         case SkImageEncoder::kBMP_Type:
         case SkImageEncoder::kGIF_Type:
         case SkImageEncoder::kJPEG_Type:
         case SkImageEncoder::kPNG_Type:
             break;
         default:
             return nullptr;
     }
     return new SkImageEncoder_CG(t);
 }
 
 static SkImageEncoder_EncodeReg gEReg(sk_imageencoder_cg_factory);
+#endif
 
-class SkPNGImageEncoder_CG : public SkImageEncoder_CG {
-public:
-    SkPNGImageEncoder_CG()
-        : SkImageEncoder_CG(kPNG_Type) {
-    }
-};
-
-DEFINE_ENCODER_CREATOR(PNGImageEncoder_CG);
+SkImageEncoder* CreateImageEncoder_CG(SkImageEncoder::Type type) {
+    return new SkImageEncoder_CG(type);
+}
 
 #endif//defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS)