change write-image to use pipeverbs like everyone else, and add test

src/pipe/SkPipeCanvas.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPipeCanvas_DEFINED
 #define SkPipeCanvas_DEFINED
 
 #include "SkCanvas.h"
 #include "SkDeduper.h"
 #include "SkImage.h"
 #include "SkPipe.h"
 #include "SkTypeface.h"
 #include "SkWriteBuffer.h"
 
 class SkPipeCanvas;
 class SkPipeWriter;
 
 template <typename T> class SkTIndexSet {
 public:
     void reset() { fArray.reset(); }
 
     // returns the found index or 0
-    int find(const T& key) {
+    int find(const T& key) const {
         const Rec* stop = fArray.end();
         for (const Rec* curr = fArray.begin(); curr < stop; ++curr) {
             if (key == curr->fKey) {
                 return curr->fIndex;
             }
         }
         return 0;
     }
 
     // returns the new index
@@ skipping 20 matching lines @@
         fImages.reset();
         fPictures.reset();
         fTypefaces.reset();
         fFactories.reset();
     }
 
     void setCanvas(SkPipeCanvas* canvas) { fPipeCanvas = canvas; }
     void setStream(SkWStream* stream) { fStream = stream; }
     void setTypefaceSerializer(SkTypefaceSerializer* tfs) { fTFSerializer = tfs; }
 
+    // returns 0 if not found
+    int findImage(SkImage* image) const { return fImages.find(image->uniqueID()); }
+
     int findOrDefineImage(SkImage*) override;
     int findOrDefinePicture(SkPicture*) override;
     int findOrDefineTypeface(SkTypeface*) override;
     int findOrDefineFactory(SkFlattenable*) override;
 
 private:
     SkPipeCanvas*           fPipeCanvas = nullptr;
     SkWStream*              fStream = nullptr;
 
     SkTypefaceSerializer*   fTFSerializer = nullptr;
@@ skipping 80 matching lines @@
     SkPipeDeduper*  fDeduper;
     SkWStream*      fStream;
 
     friend class SkPipeWriter;
 
     typedef SkCanvas INHERITED;
 };
 
 
 #endif