add /img/n/m endpoint to skiaserve

tools/skiaserve/Request.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 Request_DEFINED
 #define Request_DEFINED
 
@@ skipping 11 matching lines @@
 
 struct UploadContext {
     SkDynamicMemoryWStream fStream;
     MHD_PostProcessor* fPostProcessor;
     MHD_Connection* connection;
 };
 
 struct Request {
     Request(SkString rootUrl); 
 
-    SkData* drawToPng(int n);
+    // draws to skia draw op N, highlighting the Mth batch(-1 means no highlight)
+    SkData* drawToPng(int n, int m = -1);
     SkCanvas* getCanvas();
     SkBitmap* getBitmapFromCanvas(SkCanvas* canvas);
     bool enableGPU(bool enable);
     bool hasPicture() const { return SkToBool(fPicture.get()); }
     int getLastOp() const { return fDebugCanvas->getSize() - 1; }
 
     bool initPictureFromStream(SkStream*);
 
     // Returns the json list of ops as an SkData
     SkData* getJsonOps(int n);
 
     // Returns a json list of batches as an SkData
     SkData* getJsonBatchList(int n);
 
     // Returns json with the viewMatrix and clipRect
     SkData* getJsonInfo(int n);
 
     // TODO probably want to make this configurable
     static const int kImageWidth;
     static const int kImageHeight;
 
     UploadContext* fUploadContext;
     SkAutoTUnref<SkDebugCanvas> fDebugCanvas;
     UrlDataManager fUrlDataManager;
     
 private:
     SkData* writeCanvasToPng(SkCanvas* canvas);
-    void drawToCanvas(int n);
+    void drawToCanvas(int n, int m = -1);
     SkSurface* createCPUSurface();
     SkSurface* createGPUSurface();
     GrAuditTrail* getAuditTrail(SkCanvas*);
     void cleanupAuditTrail(SkCanvas*);
     
     SkAutoTUnref<SkPicture> fPicture;
     SkAutoTDelete<GrContextFactory> fContextFactory;
     SkAutoTUnref<SkSurface> fSurface;
     bool fGPUEnabled;
 };
 
 #endif