Enable generating SkImage with the same uniqueID in SkImageGenerator subclass

include/core/SkImageGenerator.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageGenerator_DEFINED
 #define SkImageGenerator_DEFINED
 
@@ skipping 233 matching lines @@
             sk_throw();
         }
     }
     void generateBitmap(SkBitmap* bm, const SkImageInfo& info) {
         if (!this->tryGenerateBitmap(bm, &info, nullptr)) {
             sk_throw();
         }
     }
 
 protected:
-    SkImageGenerator(const SkImageInfo& info);
+    enum {
+        kNeedNewImageUniqueID = 0
+    };
+
+    SkImageGenerator(const SkImageInfo& info, uint32_t uniqueId = kNeedNewImageUniqueID);
 
     virtual SkData* onRefEncodedData(SK_REFENCODEDDATA_CTXPARAM);
 
     virtual bool onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes,
                              SkPMColor ctable[], int* ctableCount);
 
     virtual bool onQueryYUV8(SkYUVSizeInfo*, SkYUVColorSpace*) const {
         return false;
     }
     virtual bool onGetYUV8Planes(const SkYUVSizeInfo&, void*[3] /*planes*/) {
@@ skipping 17 matching lines @@
     const SkImageInfo fInfo;
     const uint32_t fUniqueID;
 
     // This is our default impl, which may be different on different platforms.
     // It is called from NewFromEncoded() after it has checked for any runtime factory.
     // The SkData will never be NULL, as that will have been checked by NewFromEncoded.
     static SkImageGenerator* NewFromEncodedImpl(SkData*);
 };
 
 #endif  // SkImageGenerator_DEFINED