Enable generating SkImage with the same uniqueID in SkImageGenerator subclass

src/core/SkImageGenerator.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImageGenerator.h"
 #include "SkNextID.h"
 
-SkImageGenerator::SkImageGenerator(const SkImageInfo& info)
+SkImageGenerator::SkImageGenerator(const SkImageInfo& info, uint32_t uniqueID)
     : fInfo(info)
-    , fUniqueID(SkNextID::ImageID())
+    , fUniqueID(kNeedNewImageUniqueID == uniqueID ? SkNextID::ImageID() : uniqueID)
 {}
 
 bool SkImageGenerator::getPixels(const SkImageInfo& info, void* pixels, size_t rowBytes,
                                  SkPMColor ctable[], int* ctableCount) {
     if (kUnknown_SkColorType == info.colorType()) {
         return false;
     }
     if (nullptr == pixels) {
         return false;
     }
@@ skipping 186 matching lines @@
     if (nullptr == data) {
         return nullptr;
     }
     if (gFactory) {
         if (SkImageGenerator* generator = gFactory(data)) {
             return generator;
         }
     }
     return SkImageGenerator::NewFromEncodedImpl(data);
 }